CSS Snapshot 2021

CSS Snapshot 2021
CSS Snapshot 2021
W3C Group Note
21 December 2021
More details about this document
This version:
Latest published version:
Editor's Draft:
History:
Feedback:
CSSWG Issues Repository
Editors:
Tab Atkins Jr.
Google
Elika J. Etemad / fantasai
Invited Expert
Florian Rivoal
Invited Expert
Suggest an Edit for this Spec:
GitHub Editor
W3C
MIT
ERCIM
Keio
Beihang
). W3C
liability
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and
permissive document license
rules apply.
Abstract
This document collects together into one definition all the specs that

together form the current state of Cascading Style Sheets (CSS) as of 2021.
The primary audience is CSS implementers, not CSS authors, as this definition
includes modules by specification stability, not Web browser adoption rate.
CSS
is a language for describing the rendering of structured documents
(such as HTML and XML)
on screen, on paper, etc.
Status of this document
This section describes the status of this document at the time of its publication.
A list of current W3C publications
and the latest revision of this technical report
can be found in the
W3C technical reports index at https://www.w3.org/TR/.
This document was published
by the
CSS Working Group
as a Group Note
using the
Note track
Group Notes are not endorsed by W3C nor its Members.
Please send feedback
by
filing issues in GitHub
(preferred),
including the spec code “css-2021” in the title, like this:
“[css-2021]
…summary of comment…
”.
All issues and comments are
archived
Alternately, feedback can be sent to the (
archived
) public mailing list
www-style@w3.org
This document is governed by the
2 November 2021 W3C Process Document
The
W3C Patent Policy
does not carry any licensing requirements or commitments on this document.
1.
Introduction
When the first CSS specification was published,
all of CSS was contained in one document that defined CSS Level 1.
CSS Level 2 was defined also by a single, multi-chapter document.
However for CSS beyond Level 2,
the CSS Working Group chose to adopt a modular approach,
where each module defines a part of CSS,
rather than to define a single monolithic specification.
This breaks the specification into more manageable chunks
and allows more immediate, incremental improvement to CSS.
Since different CSS modules are at different levels of stability,
the CSS Working Group has chosen to publish this profile
to define the current scope and state of Cascading Style Sheets as of 2021.
This profile includes only specifications that we consider stable
and
for which we have enough implementation experience that we are sure of that stability.
Note:
This is not intended to be a CSS Desktop Browser Profile:
inclusion in this profile is based on feature stability only
and not on expected use or Web browser adoption.
This profile defines CSS in its most complete form.
Note:
Although we don’t anticipate significant changes to the specifications that form this snapshot,
their inclusion does not mean they are frozen.
The Working Group will continue to address problems as they are found in these specs.
Implementers should monitor
www-style
and/or the
CSS Working Group Blog
for any resulting changes, corrections, or clarifications.
1.1.
Background: The W3C Process and CSS
This section is non-normative.
In the
W3C Process
a Recommendation-track document passes through three levels of stability,
summarized below:
Working Draft (WD)
This is the design phase of a W3C spec.
The WG iterates the spec in response to internal and external feedback.
The first official Working Draft is designated the “First Public Working Draft” (FPWD).
In the CSSWG, publishing FPWD indicates that the Working Group as a whole has agreed to work on the module,
roughly as scoped out and proposed in the editor’s draft.
The transition to the next stage is sometimes called “Last Call Working Draft” (LCWD) phase.
The CSSWG transitions Working Drafts once we have resolved all known issues,
and can make no further progress without feedback from building tests and implementations.
This “Last Call for Comments” sets a deadline for reporting any outstanding issues,
and requires the WG to specially track and address incoming feedback.
The comment-tracking document is the Disposition of Comments (DoC).
It is submitted along with an updated draft for the Director’s approval,
to demonstrate wide review and acceptance.
Candidate Recommendation (CR)
This is the testing phase of a W3C spec.
Notably, this phase is about using tests and implementations to test the specification:
it is not about testing the implementations.
This process often reveals more problems with the spec,
and so a Candidate Recommendation will morph over time in response to implementation and testing feedback,
though usually less so than during the design phase (WD).
Demonstration of two correct, independent implementations of each feature is required to exit CR,
so in this phase the WG builds a test suite and generates implementation reports.
The transition to the next stage is “Proposed Recommendation” (PR).
During this phase the W3C Advisory Committee must approve the transition to REC.
Recommendation (REC)
This is the completed state of a W3C spec and represents a maintenance phase.
At this point the WG only maintains an errata document
and occasionally publishes an updated edition that incorporates the errata back into the spec.
An
Editor’s Draft
is effectively a live copy of the editors’ own working copy.
It may or may not reflect Working Group consensus,
and can at times be in a self-inconsistent state.
(Because the publishing process at W3C is time-consuming and onerous,
the
Editor’s Draft
is usually the best (most up-to-date) reference for a spec.
Efforts are currently underway to reduce the friction of publishing,
so that official drafts will be regularly up-to-date
and
Editor’s Drafts
can return to their original function as scratch space.)
2.
Classification of CSS Specifications
A list of all CSS modules, stable and in-progress,
and their statuses
can be found at the
CSS Current Work page
2.1.
Cascading Style Sheets (CSS) — The Official Definition
As of 2021,
Cascading Style Sheets (CSS)
is defined by the following
specifications.
CSS Level 2, latest revision
(including errata)
[CSS2]
This defines the core of CSS, parts of which are overridden by later specifications.
We recommend in particular reading
Chapter 2
which introduces some of the basic concepts of CSS
and its design principles.
CSS Syntax Level 3
[CSS-SYNTAX-3]
Replaces CSS2§4.1, CSS2§4.2, CSS2§4.4, and CSS2§G,
redefining how CSS is parsed.
CSS Style Attributes
[CSS-STYLE-ATTR]
Defines how CSS declarations can be embedded in markup attributes.
Media Queries Level 3
[CSS3-MEDIAQUERIES]
Replaces CSS2§7.3 and expands on the syntax for media-specific styles.
CSS Conditional Rules Level 3
[CSS-CONDITIONAL-3]
Extends and supersedes CSS2§7.2,
updating the definition of
@media
rules to allow nesting
and introducing the
@supports
rule for feature-support queries.
Selectors Level 3
[SELECTORS-3]
Replaces CSS2§5 and CSS2§6.4.3, defining an extended range of selectors.
CSS Namespaces
[CSS3-NAMESPACE]
Introduces an
@namespace
rule to allow namespace-prefixed selectors.
CSS Cascading and Inheritance Level 4
[CSS-CASCADE-4]
Extends and supersedes CSS2§1.4.3 and CSS2§6, as well as
[CSS-CASCADE-3]
Describes how to collate style rules and assign values to all properties on all elements.
By way of cascading and inheritance, values are propagated for all properties on all elements.
CSS Values and Units Level 3
[CSS-VALUES-3]
Extends and supersedes CSS2§1.4.2.1, CSS2§4.3, and CSS2§A.2.1–3,
defining CSS’s property definition syntax
and expanding its set of units.
CSS Custom Properties for Cascading Variables Module Level 1
[CSS-VARIABLES-1]
Introduces cascading variables as a new primitive value type that is accepted by all CSS properties,
and custom properties for defining them.
CSS Box Model Level 3
[CSS-BOX-3]
Replaces CSS2§8.1, §8.2, §8.3 (but not §8.3.1), and §8.4.
CSS Color Level 3
[CSS-COLOR-3]
Extends and supersedes CSS2§4.3.6, CSS2§14.1, and CSS2§18.2,
introducing an extended range of color values.
Also introduces the
opacity
property.
CSS Backgrounds and Borders Level 3
[CSS-BACKGROUNDS-3]
Extends and supersedes CSS2§8.5 and CSS2§14.2,
providing more control of backgrounds and borders,
including layered background images,
image borders,
and drop shadows.
CSS Images Level 3
[CSS-IMAGES-3]
Redefines and incorporates the external 2D image value type,
introduces native 2D gradients,
and adds additional controls for replaced element sizing and rendering.
CSS Fonts Level 3
[CSS-FONTS-3]
Extends and supersedes CSS2§15
and provides more control over font choice and feature selection.
CSS Writing Modes Level 3
[CSS-WRITING-MODES-3]
Defines CSS support for various international writing modes,
such as left-to-right (e.g. Latin or Indic),
right-to-left (e.g. Hebrew or Arabic),
bidirectional (e.g. mixed Latin and Arabic) and vertical (e.g. Asian scripts).
Replaces and extends CSS2§8.6 and §9.10.
CSS Multi-column Layout Level 1
[CSS-MULTICOL-1]
Introduces multi-column flows to CSS layout.
CSS Flexible Box Module Level 1
[CSS-FLEXBOX-1]
Introduces a flexible linear layout model for CSS.
CSS User Interface Module Level 3
[CSS-UI-3]
Extends and supersedes CSS2§18.1 and CSS2§18.4,
defining
cursor
outline
, and several new CSS features that also enhance the user interface.
CSS Containment Module Level 1
[CSS-CONTAIN-1]
Introduces the
contain
property,
which enforces the independent CSS processing of an element’s subtree
in order to enable heavy optimizations by user agents when used well.
CSS Transforms Level 1
[CSS-TRANSFORMS-1]
Introduces coordinate-based graphical transformations to CSS.
CSS Compositing and Blending Level 1
[COMPOSITING]
Defines the compositing and blending of overlaid content
and introduces features to control their modes.
CSS Easing Functions Level 1
[CSS-EASING-1]
Describes a way for authors to define a transformation
that controls the rate of change of some value.
Applied to animations,
such transformations can be used to produce animations
that mimic physical phenomena such as momentum
or to cause the animation to move in discrete steps producing robot-like movement.
CSS Counter Styles Level 3
[CSS-COUNTER-STYLES-3]
Introduces the
@counter-style
rule,
which allows authors to define their own custom counter styles
for use with CSS list-marker and generated-content counters
[CSS-LISTS-3]
It also predefines a set of common counter styles,
including the ones present in CSS2 and CSS2.1.
2.2.
Fairly Stable Modules with limited implementation experience
The following modules have completed design work,
and are fairly stable,
but have not received much testing and implementation experience yet.
We hope to incorporate them into the
official definition of CSS
in a future snapshot.
Media Queries Level 4
[MEDIAQUERIES-4]
Extends and supersedes
[CSS3-MEDIAQUERIES]
expanding the syntax, deprecating most media types,
and introducing new media features.
CSS Color Level 4
[CSS-COLOR-4]
Extends and supersedes
[CSS-COLOR-3]
further expanding the range of colors expressible in CSS.
CSS Display Module Level 3
[CSS-DISPLAY-3]
Replaces CSS2§9.1.2, §9.2.1 (but not §9.2.1.1), §9.2.2 (but not §9.2.2.1), §9.2.3, and §9.2.4 (and lays the foundations for replacing §9.7),
defining how the CSS formatting box tree is generated
from the document element tree
and defining the
display
property that controls it.
CSS Writing Modes Level 4
[CSS-WRITING-MODES-4]
Extends and supersedes
[CSS-WRITING-MODES-3]
adding more options for vertical writing.
CSS Fragmentation Module Level 3
[CSS-BREAK-3]
Describes the fragmentation model that partitions a flow into pages, columns, or regions
and defines properties that control it.
Extends and supersedes CSS2§13.3.
CSS Box Alignment Module Level 3
[CSS-ALIGN-3]
Introduces properties to control the alignment of boxes
within their containers in the various CSS box layout models:
block layout, table layout, flex layout, and grid layout.
CSS Shapes Module Level 1
[CSS-SHAPES-1]
Extends floats (CSS2§9.5) to effect non-rectangular wrapping shapes.
CSS Text Module Level 3
[CSS-TEXT-3]
Extends and supersedes CSS2§16 excepting §16.2,
defining properties for text manipulation and specifying their processing model.
It covers line breaking, justification and alignment, white space handling, and text transformation.
CSS Text Decoration Level 3
[CSS-TEXT-DECOR-3]
Extends and supersedes CSS2§16.3,
providing more control over text decoration lines
and adding the ability to specify text emphasis marks
and text shadows.
CSS Counter Styles Level 3
[CSS-COUNTER-STYLES-3]
Expands the possible values of

and provides an
@counter-style
syntax for customized counter styles.
CSS Masking Level 1
[CSS-MASKING-1]
Replaces CSS2§11.1.2
and introduces more powerful ways of clipping and masking content.
CSS Scroll Snap Module Level 1
[CSS-SCROLL-SNAP-1]
Contains features to control panning and scrolling behavior with “snap positions”.
CSS Speech Module Level 1
[CSS-SPEECH-1]
Replaces CSS2§A,
overhauling the (non-normative) speech rendering chapter.
CSS Scrollbars Styling Module Level 1
[CSS-SCROLLBARS-1]
Defines properties to influence the visual styling of scrollbars,
introducing controls for their color and width.
2.3.
Modules with Rough Interoperability
Although the following modules have been widely deployed with
rough interoperability
their details are not fully worked out or sufficiently well-specified
and they need more testing and bugfixing.
We hope to incorporate them into the
official definition of CSS
in a future snapshot.
CSS Transitions Level 1
[CSS-TRANSITIONS-1]
and
CSS Animations Level 1
[CSS-ANIMATIONS-1]
Introduces mechanisms for transitioning the computed values of CSS properties over time.
CSS Grid Layout Module Level 1
[CSS-GRID-1]
Introduces a two-dimensional grid-based layout system,
optimized for user interface design.
In the grid layout model, the children of a grid container
can be positioned into arbitrary slots in a predefined flexible or fixed-size layout grid.
CSS Grid Layout Module Level 2
[CSS-GRID-2]
Extends and supersedes
[CSS-GRID-1]
introducing “subgrids” for managing nested markup in a shared grid framework.
CSS Will Change Level 1
[CSS-WILL-CHANGE-1]
Introduces a performance hint property called
will-change
Filter Effects Module Level 1
[FILTER-EFFECTS-1]
Introduces filter effects as a way of processing an element’s rendering before it is displayed in the document.
CSS Font Loading Module Level 3
[CSS-FONT-LOADING-3]
Introduces events and interfaces used for dynamically loading font resources.
CSS Box Sizing Level 3
[CSS-SIZING-3]
Overlays and extends CSS§10.,
expanding the value set of the sizing properties,
introducing more precise sizing terminology,
and defining with more precision and detail
various automatic sizing concepts only vaguely defined in CSS2.
CSS Transforms Level 2
[CSS-TRANSFORMS-2]
Builds upon
[CSS-TRANSFORMS-1]
to add new transform functions and properties for three-dimensional transforms,
and convenience functions for simple transforms.
CSS Lists and Counters Module Level 3
[CSS-LISTS-3]
Contains CSS features related to list counters:
styling them,
positioning them,
and manipulating their value.
CSS Logical Properties and Values Level 1
[CSS-LOGICAL-1]
Introduces logical properties and values
that provide the author with the ability to control layout through logical,
rather than physical,
direction and dimension mappings.
Also defines logical properties and values for the features defined in
[CSS2]
These properties are writing-mode relative equivalents
of their corresponding physical properties.
CSS Positioned Layout Module Level 3
[CSS-POSITION-3]
Contains defines coordinate-based positioning and offsetting schemes of CSS:
relative positioning
sticky positioning
absolute positioning
and
fixed positioning
Resize Observer
[RESIZE-OBSERVER-1]
This specification describes an API for observing changes to element’s principal box’s size.
Web Animations
[WEB-ANIMATIONS-1]
Defines a model for synchronization and timing of changes to the presentation of a Web page.
Also defines an application programming interface for interacting with this model.
CSS Fonts Module Level 4
[CSS-FONTS-4]
Extends and supersedes CSS Fonts 3
and provides more control over font choice and feature selection,
including support for OpenType variations.
2.4.
CSS Levels
Cascading Style Sheets does not have versions in the traditional sense;
instead it has
levels
. Each level of CSS builds on the previous,
refining definitions and adding features. The feature set of each higher
level is a superset of any lower level, and the behavior allowed for a given
feature in a higher level is a subset of that allowed in the lower levels.
A user agent conforming to a higher level of CSS is thus also conformant to
all lower levels.
CSS Level 1
The CSS Working Group considers the
CSS1 specification
to be
obsolete.
CSS Level 1
is defined as all the features defined
in the CSS1 specification (properties, values, at-rules, etc), but using
the syntax and definitions in the
CSS2.1 specification
CSS Style Attributes
defines its inclusion in element-specific style attributes.
CSS Level 2
Although the
CSS2 specification
is technically a W3C Recommendation, it passed into the Recommendation stage
before the W3C had defined the Candidate Recommendation stage. Over time
implementation experience and further review has brought to light many problems
in the CSS2 specification, so instead of expanding an already
unwieldy
errata list
, the CSS Working Group chose to define
CSS Level 2
Revision 1
(CSS2.1). In case of any conflict between the two specs
CSS2.1 contains the definitive definition.
Once CSS2.1 became Candidate Recommendation—effectively though not
officially the same level of stability as CSS2—obsoleted the CSS2
Recommendation. Features in CSS2 that were dropped from CSS2.1 should be
considered to be at the Candidate Recommendation stage, but note that many
of these have been or will be pulled into a CSS Level 3 working draft, in
which case that specification will, once it reaches CR, obsolete the
definitions in CSS2.
The
CSS2.1 specification
defines
CSS Level 2
and the
CSS
Style Attributes specification
defines its inclusion in
element-specific style attributes.
CSS Level 3
CSS Level 3
builds on CSS Level 2 module by module, using the CSS2.1
specification as its core. Each module adds functionality and/or
replaces part of the CSS2.1 specification. The CSS Working Group
intends that the new CSS modules will not contradict the CSS2.1
specification: only that they will add functionality and refine
definitions. As each module is completed, it will be plugged in to
the existing system of CSS2.1 plus previously-completed modules.
From this level on modules are levelled independently: for example
Selectors Level 4 may well be completed before CSS Line Module Level 3.
Modules with no
CSS Level 2
equivalent start at Level 1;
modules that update features that existed in
CSS Level 2
start at Level 3.
CSS Level 4
and beyond
There is no CSS Level 4.
Independent modules can reach level 4 or beyond,
but CSS the language no longer has levels.
("CSS Level 3" as a term is used only to differentiate it from the previous monolithic versions.)
2.5.
CSS Profiles
Not all implementations will implement all functionality defined in CSS.
In the past, the Working Group published a few Profiles,
which were meant to define the minimal subset of CSS
that various classes of user agents were expected to support.
This effort has been discontinued,
as the Working Group was not finding it effective or useful,
and the profiles previously defined are now unmaintained.
Note:
Partial implementations of CSS, even if that subset is an official profile,
must follow the forward-compatible parsing rules for
partial implementations
3.
Requirements for Responsible Implementation of CSS
The following sections define several conformance requirements
for implementing CSS responsibly,
in a way that promotes interoperability in the present and future.
3.1.
Partial Implementations
So that authors can exploit the forward-compatible parsing rules to assign fallback values,
CSS renderers
must
treat as invalid
(and
ignore as appropriate
any at-rules, properties, property values, keywords, and other syntactic constructs
for which they have no usable level of support
In particular, user agents
must not
selectively ignore
unsupported property values and honor supported values in a single multi-value property declaration:
if any value is considered invalid (as unsupported values must be),
CSS requires that the entire declaration be ignored.
3.2.
Implementations of Unstable and Proprietary Features
To avoid clashes with future stable CSS features,
the CSSWG recommends the following best practices for the implementation of
unstable
features and
proprietary extensions
to CSS:
3.2.1.
Experimentation and Unstable Features
Implementations of
unstable
features
that are described in W3C specifications
but are not interoperable
should not be released broadly for general use;
but may be released for limited, experimental use in controlled environments.
Why?
We want to allow both authors and implementors to experiment with the feature and give feedback,
but prevent authors from relying on them in production websites
and thereby accidentally "locking in" (through content dependence)
certain syntax or behavior that might change later.
For example,
a UA could release an
unstable
features for experimentation
through beta or other testing-stage builds;
behind a hidden configuration flag;
behind a switch enabled only for specific testing partners;
or through some other means of limiting dependent use.
A CSS feature is considered
unstable
until
its specification has reached the Candidate Recommendation (CR) stage in the W3C process.
In exceptional cases,
the CSSWG may additionally, by an officially-recorded resolution,
add pre-CR features to the set that are considered safe to release for broad use.
See
§ 4 Safe to Release pre-CR Exceptions
Note:
Vendors should consult the WG explicitly and not make assumptions on this point,
as a pre-CR spec that hasn’t changed in awhile is usually more out-of-date than stable.
3.2.2.
Proprietary and Non-standardized Features
To avoid clashes with future CSS features,
the CSS2.1 specification reserves a
prefixed syntax
[CSS2]
for proprietary and experimental extensions to CSS.
A CSS feature is a
proprietary extension
if it is meant for use
in a closed environment accessible only to a single vendor’s user agent(s).
A UA should support such
proprietary extensions
only through a vendor-
prefixed
syntax
and not expose them to open (multi-UA) environments such as the World Wide Web.
Why?
The prefixing requirement allows shipping specialized features in closed environments
without conflicting with future additions to standard CSS.
The restriction on exposure to open systems is to prevent
accidentally causing the public CSS environment
to depend on an unstandardized
proprietary extensions
For example,
Firefox’s XUL-based UI, Apple’s iTunes UI, and Microsoft’s Universal Windows Platform app
use extensions to CSS implemented by their respective UAs.
So long as these UAs do not allow Web content to access these features,
they do not provide an opportunity for such content
to become dependent on their
proprietary extensions
Even if a feature is intended to eventually be used in the Web,
if it hasn’t yet been standardized
it should still not be exposed to the Web.
3.2.3.
Market Pressure and De Facto Standards
If a feature is
unstable
(i.e. the spec has not yet stabilized), but
at least three UAs implement the feature
or
a UA has broken the other rules and shipped for broad use
an
unstable
or otherwise non-standard feature in a production release),
and
the implementations have rough interoperability,
and
the CSS Working Group has recorded consensus
that this feature should exist and be released,
implementers may ship that feature
unprefixed
in broad-release builds.
Rough interoperability
is satisfied by a subjective judgment
that even though there may be differences,
the implementations are sufficiently similar
to be used in production websites for a substantial number of use cases.
Note that the CSSWG must still be consulted to ensure coordination across vendors
and to ensure coherency review by the CSS experts from each vendor.
Note also that
rough interoperability
still usually means
painful lack of interop in edge (or not-so-edge) cases,
particularly because details have not been ironed out through the standards review process.
Why?
If a feature is sufficiently popular that three or more browsers have implemented it before it’s finished standardization,
this clause allows releasing the pressure to ship.
Also, if a feature has already escaped into the wild and sites have started depending on it,
pretending it’s still “experimental” doesn’t help anyone.
Allowing others to ship unprefixed recognizes that the feature is now de facto standardized
and encourages authors to write cross-platform code.
3.2.3.1.
Vendor-prefixing Unstable Features
When exposing such a standards-track
unstable
feature to the Web in a production release,
implementations should support
both
vendor-prefixed
and unprefixed syntaxes
for the feature.
Once the feature has stabilized and the implementation is updated to match interoperable behavior,
support for the
vendor-prefixed
syntax should be removed.
Why?
This is recommended so that authors can use the unprefixed syntax to target all implementations,
but when necessary, can target specific implementations
to work around incompatibilities among implementations
as they get ironed out through the standards/bugfixing process.
The lack of a phase
where only the prefixed syntax is supported
greatly reduces the risk of stylesheets
being written with only the vendor-prefixed syntax.
This in turn allows UA vendors to retire
their prefixed syntax once the feature is stable,
with a lower risk of breaking existing content.
It also reduces the need occasionally felt by some vendors
to support a feature with the prefix of another vendor,
due to content depending on that syntax.
Anyone promoting
unstable
features to authors
should document them using their standard unprefixed syntax,
and avoid encouraging the use of the
vendor-prefixed
syntax
for any purpose other than working around implementation differences.
3.2.3.2.
Preserving the Openness of CSS
In order to preserve the open nature of CSS as a technology,
vendors should make it possible for other implementors
to freely implement any features that they do ship.
To this end, they should provide spec-editing and testing resources
to complete standardization of such features,
and avoid other obstacles (e.g., platform dependency, licensing restrictions)
to their competitors shipping the feature.
3.3.
Implementations of CR-level Features
Once a specification reaches the Candidate Recommendation stage,
implementers should release an
unprefixed
implementation
of any CR-level feature they can demonstrate
to be correctly implemented according to spec,
and should avoid exposing a prefixed variant of that feature.
To establish and maintain the interoperability of CSS across
implementations, the CSS Working Group requests that non-experimental
CSS renderers submit an implementation report (and, if necessary, the
testcases used for that implementation report) to the W3C before
releasing an unprefixed implementation of any CSS features. Testcases
submitted to W3C are subject to review and correction by the CSS
Working Group.
Further information on submitting testcases and implementation reports
can be found from on the CSS Working Group’s website at
Questions should be directed to the
public-css-testsuite@w3.org
mailing list.
4.
Safe to Release pre-CR Exceptions
The following features have been explicitly and proactively cleared
by the CSS Working Group for broad release
prior to the spec reaching Candidate Recommendation.
See
§ 3.2.1 Experimentation and Unstable Features
The flow-relative equivalents of
the sizing properties (
width
height
, etc.),
the border properties,
the margin and padding properties.
See
explanation
and
specification
The
min-content
and
max-content
keywords of the sizing properties.
See
decision
and
specification
The
conic-gradient()
gradient notation. See
decision
The
aspect-ratio
property.
[CSS-SIZING-4]
The following features have been explicitly and retroactively cleared
by the CSS Working Group for broad release
prior to the spec reaching Candidate Recommendation:
Everything in
CSS Animations Level 1
and
CSS Transitions Level 1
The
:dir()
:lang()
, and
:focus-within
pseudo-classes from
[SELECTORS-4]
5.
Indices
These sections are non-normative.
5.1.
Terms Index
100...900 weight values
1st
2d matrix
2nd
3rd
4th
absolute length
absolutely positioned element
abstract dimensions
activeborder
activecaption
active duration
actual value
actual values
additive tuple
adjoining
adjoining margins
advance measure
after-change style
aliceblue
aligned subtree
alignment baseline
alignment container
alignment context
alignment subject
'all' media group
all-petite-caps
all-small-caps
alphabetic baseline
ambiguous image url
an+b
ancestor
anchor
anchor unit
animation origin
animation-tainted
anonymous
in css-display-3, for CSS
in css2
anonymous box
anonymous inline boxes
antiquewhite
apply to
appworkspace
aqua
in css-color-3
in css-color-3
aquamarine
are a valid escape
as conformance class
in css-fonts-3
in css-speech-1
aspect value
at-keyword
atomic inline
atomic inline box
atomic inline-level boxes
at-rule
in css-syntax-3
in css-syntax-3, for CSS
at-rules
attribute
'audio' media group
augmented grid
aural "box" model
aural box model
author
authoring tool
in css-fonts-3
in css-speech-1
author origin
author-origin
author presentational hint origin
author style sheet
auto!!font-kerning
automatic column position
automatic grid position
automatic numbering
automatic placement
automatic position
automatic row position
auto-placement
auto-placement cursor
available font faces
available grid space
avoid break values
axis-lock
axis value
azure
backdrop
background
background painting area
background positioning area
backslash escapes
baseline
baseline alignment
baseline alignment preference
baseline content-alignment
baseline self-alignment
baseline set
baseline-sharing group
baseline table
base size
bearing angle
before-change style
before flag
beige
bfc
bidi formatting characters
bidi-isolate
bidi-isolated
bidi isolation
bidi paragraph
bidirectionality
bidirectionality (bidi)
bi-orientational
bi-orientational transform
bisque
'bitmap' media group
black
in css-color-3
in css-color-3
blanchedalmond
()-block
[]-block
block
{}-block
block at-rule
block axis
block-axis
block box
block boxes
block container
block container box
block dimension
block end
block-end
block flow direction
block formatting context
block formatting context root
blockification
blockify
block layout
block-level
block-level box
block-level boxes
block-level content
block-level elements
block scripts
block size
block-size
block start
block-start
blue
in css-color-3
in css-color-3
blueviolet
blur radius
bold
bolder
boolean context
border
in css-speech-1
in css2
border box
border-box
border edge
border image area
border (of a box)
border radius
bottom
box
box alignment properties
box-corner
box fragment
box tree
break
brown
burlywood
buttonface
buttonhighlight
buttonshadow
buttontext
cadetblue
cancel
canonical unit
canvas
canvas background
canvas surface
captiontext
captures snap positions
cascade
in css-cascade-4
in css-speech-1
cascaded value
cascade origin
central baseline
character
in css-text-3
in css-text-decor-3
character encoding
character map
"@charset"
chartreuse
check if three code points would start an identifier
check if three code points would start an ident sequence
check if three code points would start a number
check if two code points are a valid escape
child
child combinator
child selector
chinese
chocolate
circled-lower-latin
clamp a grid area
clearance
clearance.
clipping path
clipping region
closest-side
clustered scripts
collapse
collapsed
collapsed flex item
collapsed gutter
collapsed margin
collapsed track
collapse through
collapsible white space
collapsing margin
color stop
color stop list
color transition hint
column box
column break
column gap
column height
column rule
column width
combinators
in css2
in selectors-3
combined duration
comments
common-ligatures
compatible baseline alignment preferences
compatible units
complete
completed transition
component value
composite face
computed
computed track list
computed value
computed values
concrete object size
condensed
conditional group rule
conditional import
conditionally hang
conformance
consecutive
constraint rectangle
consume a component value
consume a declaration
consume a function
consume a list of declarations
consume a list of rules
consume a name
consume an at-rule
consume an escaped code point
consume an ident-like token
consume an ident sequence
consume a number
consume a numeric token
consume a qualified rule
consume a simple block
consume a string token
consume a style block's contents
consume a token
consume a url token
consume comments
consume the next input token
consume the remnants of a bad url
contain constraint
containing block
containing block chain
containing block for all descendants
containment
content
in css-speech-1
in css2
content area
content-based minimum size
in css-flexbox-1
in css-grid-1
content box
content-box
content-distribution
content-distribution properties
content edge
content height
content language
in css-text-3
in css-text-decor-3
content (of a box)
content size suggestion
in css-flexbox-1
in css-grid-1
content width
content writing system
contextual
continuous media
'continuous' media group
convert a string to a number
coordinated self-alignment preference
coral
cornflowerblue
cornsilk
counters
counter style
counter symbol
cover constraint
crimson
cross axis
cross-axis
cross-axis baseline set
cross dimension
cross-end
cross size
cross-size
cross size property
cross-start
css bracketed range notation
css-connected
css feature queries
cssfontfacerule
css ident
in css-values-3
in css-values-3, for CSS
css identifier
in css-values-3
in css-values-3, for CSS
css ident sequence
css qualified name
css-wide keywords
cubic bézier easing function
currentcolor
current input code point
current input token
current transformation matrix
current value
cursive
cursive script
custom property
cyan
darkblue
darkcyan
darkgoldenrod
darkgray
darkgreen
darkgrey
darkkhaki
darkmagenta
darkolivegreen
darkorange
darkorchid
darkred
darksalmon
darkseagreen
darkslateblue
darkslategray
darkslategrey
darkturquoise
darkviolet
declaration
in css-syntax-3, for CSS
in css2
declaration block
declared
declared value
decode
decode bytes
decorating box
deeppink
deepskyblue
default face
default namespace
default object size
default sizing algorithm
default style sheet
definite
definite column position
definite column span
definite grid position
definite grid span
definite position
definite row position
definite row span
definite size
definite span
descendant
descendant-selectors
descriptor
descriptor_declaration
descriptor declarations
destination
determine the fallback encoding
diagonal-fractions
dice
digit
dimension
dimgray
dimgrey
directional embedding
directional override
discretionary-ligatures
display
display type
distributed alignment
distribute extra space
document
in css-backgrounds-3
in css-speech-1
in css-style-attr-1
document language
document order
documents
document tree
document white space
document white space characters
dodgerblue
dominant baseline
easing function
east asian width property
effective character map
element
in css-display-3, for CSS
in css2
element tree
empty
empty float area
encapsulation contexts
end
ending point
ending shape
ending token
end time
end value
environment encoding
eof code point
escaping
establish an independent formatting context
establish an orthogonal flow
established an independent formatting context
establishes an independent formatting context
establishing an independent formatting context
exact matching
expanded
expanded name
explicit grid
explicit grid column
explicit grid properties
explicit grid row
explicit grid track
explicitly-assigned line name
extra-condensed
extra-expanded
fallback alignment
false in the negative range
fantasy
farthest-side
fetch an @import
fictional tag sequence
filter code points
filtered code points
filter primitive
filter primitive attributes
filter primitive subregion
filter primitive tree
filter region
find the matching font faces
fire a font load event
firebrick
first available font
first-baseline alignment
first-baseline content-alignment
first baselines
first-baseline self-alignment
first baseline set
first cross-axis baseline set
first formatted line
first main-axis baseline set
first symbol value
fixed sizing function
flex base size
flex basis
flex container
flex direction
flex factor
in css-flexbox-1
in css-grid-1, for grid-template-columns, grid-template-rows
flex factor sum
flex formatting context
flex fraction
flex grow factor
flexible
flexible length
in css-flexbox-1
in css-grid-1
flexible sizing function
flexible tracks
flex item
flex layout
flex-level
flex line
flex shrink factor
float area
float rules
floralwhite
flow layout
flow of an element
flow-relative
flow-relative direction
focus
following element
font_face_rule
font_face_sym
font-family
font-kerning
in css-fonts-3
in css-fonts-3
in css-fonts-3
font-relative lengths
font-size-adjust
font source
font-stretch
font-style
font-variant-caps
font-variant-east-asian
font-variant-ligatures
in css-fonts-3
in css-fonts-3
font-variant-numeric
font-variant-position
font-weight
footnote
forced break
forced break values
forced line break
forced paragraph break
forestgreen
formatting context
formatting structure
forward-compatible parsing
fragment
fragmentainer
fragmentation
fragmentation break
fragmentation container
fragmentation context
fragmentation direction
fragmentation root
fragmented flow
free space
frequency
fuchsia
in css-color-3
in css-color-3
full-size
full-size kana
full-width
in css-fonts-3
in css-text-3
fully inflexible
function
functional notation
gainsboro
general category
generate a counter
generate a counter representation
generate baselines
generated content
get an encoding
ghostwhite
go
gold
goldenrod
gradient-average-color
gradient box
gradient center
gradient function
gradient line
grapheme cluster
gray
in css-color-3
in css-color-3
graytext
green
in css-color-3
in css-color-3
greenyellow
grey
grid
grid area
grid cell
grid column
grid column line
grid container
grid formatting context
grid item
grid item placement algorithm
grid layout
grid-level
grid line
'grid' media group
grid-modified document order
grid order
grid placement
grid-placement property
grid position
grid row
grid row line
grid sizing algorithm
grid span
grid track
growth limit
guaranteed-invalid value
gutter
half-width
hang
hanging glyph
height
hex digit
highlight
highlighttext
historical-ligatures
honeydew
horizontal axis
horizontal block flow
horizontal dimension
horizontal offset
horizontal-only
horizontal script
horizontal typographic mode
horizontal writing mode
hotpink
hyphenate
hyphenation
hyphenation opportunity
hyphen-separated matching
hypothetical cross size
hypothetical fr size
hypothetical main size
ident
in css-values-3
in css-values-3, for CSS
ident code point
identifier
in css-speech-1
in css-syntax-3
in css-values-3
in css-values-3, for CSS
identifiers
identity transform function
ident sequence
ident-start code point
ignore
ignored
ignore unknown
ignore valid
illegal
implicit grid
implicit grid column
implicit grid lines
implicit grid properties
implicit grid row
implicit grid track
implicitly-assigned line name
implicitly-named area
important
import conditions
inactiveborder
inactivecaption
inactivecaptiontext
indefinite
indefinite size
independent formatting context
indianred
indigo
infinitely growable
in flow
in-flow
infobackground
infotext
inherit
inheritance
inherited property
inherited value
initial containing block
initial free space
initial representation for the counter value
initial value
inline
inline axis
inline-axis
inline base direction
inline block
inline block box
inline box
inline dimension
inline end
inline-end
inline formatting context
inline-level
inline-level box
inline-level boxes
inline-level content
inline-level elements
inline size
inline-size
inline start
inline-start
inlinification
inlinify
inner box-shadow
inner display type
inner edge
input progress value
input stream
integer
in css-speech-1
in css-values-3
intended direction
intended direction and end position
intended end position
'interactive media group
internal ruby box
internal ruby element
internal table box
internal table element
interpreter
in css-namespaces-3
in css-style-attr-1
intrinsic dimensions
intrinsic sizing function
invalid
invalid at computed-value time
invalid image
invisible
isolated sequence
isolation
italic
iteration order
ivory
japanese
jis04
jis78
jis83
jis90
justification opportunity
keyword
khaki
known
korean
last-baseline alignment
last-baseline content-alignment
last baselines
last-baseline self-alignment
last baseline set
last cross-axis baseline set
last main-axis baseline set
lavender
lavenderblush
lawngreen
laying out in-place
layout containment
layout containment box
layout-internal
left
leftover space
legacy name alias
legacy shorthand
legacy value alias
lemonchiffon
letter
in css-syntax-3
in css-text-3
in css-text-decor-3
lightblue
lightcoral
lightcyan
lighter
lightgoldenrodyellow
lightgray
lightgreen
lightgrey
lightpink
lightsalmon
lightseagreen
lightskyblue
lightslategray
lightslategrey
light source
lightsteelblue
lightyellow
lime
in css-color-3
in css-color-3
limegreen
limited max-content contribution
limited min-content contribution
linear easing function
linear timing function
line box
line break
in css-break-3
in css-text-3
line breaking
line breaking process
line-left
linen
line name
line name set
line orientation
line-over
line-relative
line-relative direction
line-right
line-under
lining-nums
list properties
list-style-image
list-style-type
loading image
local coordinate system
local url flag
logical height
logical width
longhand
longhand property
lowercase letter
magenta
main axis
main-axis
main-axis baseline set
main dimension
main-end
main size
main-size
main size property
main-start
map document language elements to table elements
margin
in css-speech-1
in css2
margin box
margin-box
margin edge
margin (of a box)
maroon
in css-color-3
in css-color-3
mask border image
mask border image area
mask image
mask layer image
mask painting area
mask-position
mask positioning area
mask-size
matches
matching transition delay
matching transition duration
matching transition-property value
matching transition timing function
max cross size
max cross size property
maximum allowed code point
max inner height
max inner width
max main size
max main size property
max track sizing function
may
media condition
media-dependent import
media feature
media groups
media query
media query list
media query modifier
media type
mediumaquamarine
mediumblue
mediumorchid
mediumpurple
mediumseagreen
mediumslateblue
mediumspringgreen
mediumturquoise
mediumvioletred
menutext
midnightblue
min cross size
min cross size property
minimum contribution
min inner height
min inner width
min main size
min main size property
mintcream
min track sizing function
mistyrose
moccasin
monolithic
monospace
multicol container
multi-col line
multicol line
multi-column container
multi-column formatting context
multi-column layout
multi-column line
multi-line flex container
multiple declarations
multiply
must
must not
name code point
named cell token
named grid area
namespace prefix
name-start code point
natural aspect ratio
natural dimension
natural end-point
natural height
natural size
natural width
navajowhite
navy
in css-color-3
in css-color-3
newline
next input code point
next input token
next-sibling combinator
no-common-ligatures
no-contextual
no-discretionary-ligatures
no-historical-ligatures
non-ascii code point
none!!font-kerning
none!!font-size-adjust
none!!font-variant-ligatures
non-negative-number
non-printable code point
non-replaced
non-replaced element
no pending font loads
normal
normal!!font-kerning
normal!!font-stretch
normal!!font-style
normal!!font-variant-caps
normal!!font-variant-east-asian
normal!!font-variant-ligatures
normal!!font-variant-numeric
normal!!font-variant-position
normal!!font-weight
normalize into a token stream
null cell token
number
in css-speech-1
in css-values-3
numeric data types
objects
object size negotiation
oblique
occupied
oldlace
oldstyle-nums
olive
in css-color-3
in css-color-3
olivedrab
operating coordinate space
optimal viewing region
optional
orange
orangered
orchid
order-modified document order
in css-display-3
in css-flexbox-1
ordinal
orthogonal
orthogonal flow
other space separators
outer box-shadow
outer display type
outer edge
out of flow
out-of-flow
output of the cascade
output progress value
over
overflow
overflow alignment
overflow columns
padding
in css-speech-1
in css2
padding box
padding-box
padding edge
padding (of a box)
page area
page box
page break
page context
page-context
paged media
'paged' media group
page selector
pagination
paint containment
paint containment box
palegoldenrod
palegreen
paleturquoise
palevioletred
papayawhip
parent
parent box
parse
parse a comma-separated list according to a css grammar
parse a comma-separated list of component values
parse a component value
parse a css stylesheet
parse a declaration
parse a list
parse a list of component values
parse a list of declarations
parse a list of rules
parse a rule
parse a style block's contents
parse a stylesheet
in css-syntax-3
in css-syntax-3
parse error
parse something according to a css grammar
parsing a list
participates in baseline alignment
pass through filter
peachpuff
pending on the environment
pending-substitution value
percentage
in css-speech-1
in css-values-3
peru
petite-caps
physical
physical bottom
physical dimensions
physical direction
physical left
physical right
physical top
physical units
pink
pixel
pixel unit
plum
positional alignment
positioned
positioned element/box
positioning scheme
positioning schemes:
possibly pending font loads
post-multiplied
post-multiply
powderblue
preceding element
pre-multiplied
pre-multiply
preserved tokens
preserved white space
primary filter primitive tree
principal block-level box
principal box
principal writing mode
propagate
propagation
proper table child
proper table row parent
property
in css-cascade-4, for CSS
in css2
property declarations
proportional-nums
proportional-width
pseudo-classes
pseudo-elements
purple
in css-color-3
in css-color-3
qualified rule
range context
recommended
reconsume the current input code point
reconsume the current input token
red
in css-color-3
in css-color-3
reference box
in css-shapes-1
in css-transforms-1
reference pixel
region break
relative length
relative positioning
relative units
remaining fragmentainer extent
remaining free space
rendered content
renderer
in css-fonts-3
in css-speech-1
replaced
replaced element
representation
required
reset-only sub-property
re-snap
resolved type
reversing-adjusted start value
reversing shortening factor
right
root
rosybrown
row group box
row groups
royalblue
ruby
rule set
rules on anonymous table objects
run-in
run-in box
run-in sequence
running transition
saddlebrown
salmon
sandybrown
sans-serif
scaled flex shrink factor
scope
screen reader
script property
scrollbar
scroll snap
scroll snap area
scroll snap container
scroll snapport
scroll snap position
seagreen
seashell
segment break
selector
in css2
in selectors-3
selector matches
self-alignment
self-alignment properties
semi-condensed
semi-expanded
semitone
separated borders model
sequence of simple selectors
serialize an value
serif
set entries
shall
shall not
shared alignment context
sheets
shorthand
shorthand properties
shorthand property
should
should not
sibling
sideways typesetting
sienna
silver
in css-color-3
in css-color-3
simple block
simple selector
in css2
in selectors-3
simplified
single-line flex container
size containment
size containment box
sizing as if empty
sizing function
skyblue
slashed-zero
slateblue
slategray
slategrey
small
small-caps
small kana
snow
soft wrap break
soft wrap opportunity
source
source document
spaces
space-separated matching
space to fill
span count
spanner
spanning element
specified size
specified size suggestion
in css-flexbox-1
in css-grid-1
specified value
specified values
'speech' media group
spread break
spread distance
springgreen
stacked-fractions
stacking context
stack level
start
starting point
starts with an identifier
starts with an ident sequence
starts with a number
starts with a valid escape
start time
start value
start with an identifier
start with an ident sequence
start with a number
statement at-rule
'static' media group
static-position containing block
static position rectangle
static-position rectangle
steelblue
step easing function
step position
steps
stop or comma
stretched
strictness value
string
strings
stroke bounding box
structural pseudo-classes
strut size
stuck on the environment
style attribute
style change event
style rule
style sheet
in css-backgrounds-3
in css-namespaces-3
in css-speech-1
style sheet!!as conformance class
in css-fonts-3
in css-speech-1
sub
subject (of selector)
subjects
subjects of the selector
sub-property
subsequent-sibling combinator
substitute a var()
super
support
in css-conditional-3, for CSS
in css-fonts-3
supports queries
switch the fontfaceset to loaded
switch the fontfaceset to loading
synthesize baseline
synthesized baseline
system font fallback
system fonts
table
table caption box
table element
table grid box
table wrapper box
tabs
tab size
tab stop
tabular container
tabular-nums
'tactile' media group
tan
target main size
teal
in css-color-3
in css-color-3
text node
text run
textual data types
in css-values-3
in css-values-3, for CSS
thistle
threeddarkshadow
threedface
threedhighlight
threedlightshadow
threedshadow
time
timing function
titling-caps
tokenization
tokenize
tokenizer
tomato
top
tracking
track list
track section
track sizing algorithm
track sizing function
traditional
transfer function element
transfer function element attributes
transferred size suggestion
in css-flexbox-1
in css-grid-1
transformable element
transformation matrix
transformed element
transitionable
transition origin
transparent
trash token
triangle
trinary
turquoise
type selector
in css2
in selectors-3
typeset sideways
typesetting sideways
typesetting upright
typeset upright
typographic character
typographic character unit
typographic letter unit
typographic mode
ua
in css-backgrounds-3
in css-speech-1
ua origin
ua-origin
ua style sheet
ultra-condensed
ultra-expanded
under
unforced break
unicase
unicode category
unicode east asian width
unicode general category
unicode script
unicode vertical orientation
universal selector
in css2
in selectors-3
unknown
unoccupied
upper-alpha-legal
uppercase letter
upright typesetting
url
use a negative sign
used value
used values
user
user agent
in css-backgrounds-3
in css-speech-1
user-agent origin
user-agent style sheet
user agent (ua)
user coordinate system
user origin
user-origin
user style sheet
uses a negative sign
valid image
validity
valid style sheet
value definition syntax
values
var() substitution
vertical axis
vertical block flow
vertical dimension
vertical offset
vertical-only
vertical orientation
vertical script
vertical typographic mode
vertical writing mode
viewport
viewport-percentage lengths
violet
visual angle unit
visual box model
visual formatting model
'visual' media group
weight
wheat
white
in css-color-3
in css-color-3
whitesmoke
white space
whitespace
white space characters
width
in css-fonts-3
in css-writing-modes-4
window
windowframe
windowtext
word separator
word-separator character
would start an identifier
would start an ident sequence
would start a number
wrap
in css-shapes-1
in css-text-3
wrapping
in css-shapes-1
in css-text-3
writing mode
x-axis
y-axis
yellow
in css-color-3
in css-color-3
yellowgreen
5.2.
Selector Index
:active
in css2
in selectors-3
::after
:after
::before
:before
:checked
:disabled
:empty
:enabled
:first
:first-child
in css2
in selectors-3
first-child
::first-letter
:first-letter
::first-line
:first-line
:first-of-type
:focus
in css2
in selectors-3
:hover
in css2
in selectors-3
:lang
in css2
in selectors-3
:lang()
:last-child
:last-of-type
:left
:link
in css2
in selectors-3
:not()
:nth-child()
:nth-last-child()
:nth-last-of-type()
:nth-of-type()
:only-child
:only-of-type
:right
:root
:target
:visited
in css2
in selectors-3
5.3.
At-Rule Index
@charset
@counter-style
@font-face
@import
@keyframes
@media
media
@page
@supports
5.4.
Property Index
--*
align-content
in css-align-3
in css-flexbox-1
align-items
in css-align-3
in css-flexbox-1
align-self
in css-align-3
in css-flexbox-1
all
animation
animation-delay
animation-direction
animation-duration
animation-fill-mode
animation-iteration-count
animation-name
animation-play-state
animation-timing-function
azimuth
background
background-attachment
background-blend-mode
background-clip
background-color
background-image
background-origin
background-position
background-repeat
background-size
border
border-bottom
border-bottom-color
border-bottom-left-radius
border-bottom-right-radius
border-bottom-style
border-bottom-width
border-collapse
border-color
border-image
border-image-outset
border-image-repeat
border-image-slice
border-image-source
border-image-width
border-left
border-left-color
border-left-style
border-left-width
border-radius
border-right
border-right-color
border-right-style
border-right-width
border-spacing
border-style
border-top
border-top-color
border-top-left-radius
border-top-right-radius
border-top-style
border-top-width
border-width
bottom
box-decoration-break
box-shadow
box-sizing
break-after
break-before
break-inside
caption-side
caret-color
clear
clip
clip-path
clip-rule
color
in css-color-3
in css-color-3
color-interpolation-filters
column-count
column-fill
column-gap
column-rule
column-rule-color
column-rule-style
column-rule-width
columns
column-span
column-width
contain
content
counter-increment
counter-reset
cue
in css-speech-1
in css2
cue-after
in css-speech-1
in css2
cue-before
in css-speech-1
in css2
cursor
direction
display
elevation
empty-cells
filter
flex
flex-basis
flex-direction
flex-flow
flex-grow
flex-shrink
flex-wrap
float
flood-color
flood-opacity
font
font-family
font-feature-settings
font-kerning
font-size
font-size-adjust
font-stretch
font-style
font-synthesis
font-variant
font-variant-caps
font-variant-east-asian
font-variant-ligatures
font-variant-numeric
font-variant-position
font-weight
gap
globalcompositeoperation
glyph-orientation-vertical
grid
grid-area
grid-auto-columns
grid-auto-flow
grid-auto-rows
grid-column
grid-column-end
grid-column-gap
grid-column-start
grid-gap
grid-row
grid-row-end
grid-row-gap
grid-row-start
grid-template
grid-template-areas
grid-template-columns
grid-template-rows
hanging-punctuation
height
hyphens
image-orientation
image-rendering
isolation
justify-content
in css-align-3
in css-flexbox-1
justify-items
justify-self
left
letter-spacing
lighting-color
line-break
line-height
list-style
list-style-image
list-style-position
list-style-type
margin
margin-bottom
margin-left
margin-right
margin-top
mask
mask-border
mask-border-mode
mask-border-outset
mask-border-repeat
mask-border-slice
mask-border-source
mask-border-width
mask-clip
mask-composite
mask-image
mask-mode
mask-origin
mask-position
mask-repeat
mask-size
mask-type
max-height
max-width
min-height
min-width
mix-blend-mode
object-fit
object-position
opacity
order
in css-display-3
in css-flexbox-1
orphans
outline
outline-color
outline-offset
outline-style
outline-width
overflow
overflow-wrap
padding
padding-bottom
padding-left
padding-right
padding-top
page-break-after
page-break-before
page-break-inside
pause
in css-speech-1
in css2
pause-after
in css-speech-1
in css2
pause-before
in css-speech-1
in css2
pitch
pitch-range
place-content
place-items
place-self
play-during
position
quotes
resize
rest
rest-after
rest-before
richness
right
row-gap
scroll-margin
scroll-margin-block
scroll-margin-block-end
scroll-margin-block-start
scroll-margin-bottom
scroll-margin-inline
scroll-margin-inline-end
scroll-margin-inline-start
scroll-margin-left
scroll-margin-right
scroll-margin-top
scroll-padding
scroll-padding-block
scroll-padding-block-end
scroll-padding-block-start
scroll-padding-bottom
scroll-padding-inline
scroll-padding-inline-end
scroll-padding-inline-start
scroll-padding-left
scroll-padding-right
scroll-padding-top
scroll-snap-align
scroll-snap-stop
scroll-snap-type
shape-image-threshold
shape-margin
shape-outside
speak
in css-speech-1
in css2
speak-as
speak-header
speak-numeral
speak-punctuation
speech-rate
stress
table-layout
tab-size
text-align
text-align-all
text-align-last
text-combine-upright
text-decoration
text-decoration-color
text-decoration-line
text-decoration-style
text-emphasis
text-emphasis-color
text-emphasis-position
text-emphasis-style
text-indent
text-justify
text-orientation
text-overflow
text-shadow
text-transform
text-underline-position
top
transform
transform-box
transform-origin
transition
transition-delay
transition-duration
transition-property
transition-timing-function
unicode-bidi
vertical-align
visibility
voice-balance
voice-duration
voice-family
in css-speech-1
in css2
voice-pitch
voice-range
voice-rate
voice-stress
voice-volume
volume
white-space
widows
width
will-change
word-break
word-spacing
word-wrap
writing-mode
z-index
5.5.
Values Index
absolute
in css-speech-1, for voice-pitch
in css-speech-1, for voice-range
in css2, for position
add
additive
alias
all
in css-multicol-1, for column-span
in css-transitions-1, for transition-property
in css-writing-modes-4, for text-combine-upright
in css2, for @media
in mediaqueries-4, for @media
allow-end
all-scroll
alpha
in css-masking-1, for mask-border-mode
in css-masking-1, for mask-mode
in css-masking-1, for mask-type
alphabetic
alternate
alternate-reverse
always
in css-scroll-snap-1, for scroll-snap-stop
in css-speech-1, for speak
in css2, for page-break-before, page-break-after, page-break-inside

in css-images-3, for image-orientation
in css-images-3, for image-orientation
anywhere
in css-text-3, for line-break
in css-text-3, for overflow-wrap
aqua
arabic-indic
armenian
in css-counter-styles-3, for
in css2
in css2, for list-style-type
attr(x)
aural
auto
in css-align-3, for align-self
in css-align-3, for justify-self
in css-backgrounds-3, for background-size
in css-backgrounds-3, for border-image-width
in css-break-3, for break-before, break-after
in css-break-3, for break-inside, page-break-inside
in css-counter-styles-3, for @counter-style/range
in css-counter-styles-3, for @counter-style/speak-as
in css-flexbox-1, for align-items, align-self
in css-flexbox-1, for flex-basis
in css-grid-1, for
in css-grid-1, for grid-template-columns, grid-template-rows
in css-images-3, for image-rendering
in css-multicol-1, for column-count
in css-multicol-1, for column-fill
in css-multicol-1, for column-width
in css-scroll-snap-1, for scroll-padding, scroll-padding-inline, scroll-padding-inline-start, scroll-padding-inline-end, scroll-padding-block, scroll-padding-block-start, scroll-padding-block-end
in css-speech-1, for speak
in css-speech-1, for voice-duration
in css-text-3, for hyphens
in css-text-3, for line-break
in css-text-3, for text-align-last
in css-text-3, for text-justify
in css-text-decor-3, for text-underline-position
in css-ui-3, for caret-color
in css-ui-3, for cursor
in css-will-change-1, for will-change
in css2, for , , ,
in css2, for clip
in css2, for height
in css2, for overflow
in css2, for page-break-before, page-break-after, page-break-inside
in css2, for table-layout
in css2, for top, right, bottom, left
in css2, for width
in css2, for z-index
in filter-effects-1, for color-interpolation-filters
auto-fill
auto-fit
[ auto-flow && dense? ] <'grid-auto-rows'>? / <'grid-template-columns'>
avoid
in css-break-3, for break-before, break-after
in css-break-3, for break-inside, page-break-inside
in css2, for page-break-before, page-break-after, page-break-inside
avoid-column
in css-break-3, for break-before, break-after
in css-break-3, for break-inside, page-break-inside
avoid-page
in css-break-3, for break-before, break-after
in css-break-3, for break-inside, page-break-inside
avoid-region
in css-break-3, for break-before, break-after
in css-break-3, for break-inside, page-break-inside
backwards
balance
balance-all
baseline
in css-align-3, for justify-self, justify-items, align-content, align-self, align-items,
in css-flexbox-1, for align-items, align-self
in css2, for vertical-align

bengali
bidi-override
black
blink
in css-text-decor-3, for text-decoration-line
in css2, for text-decoration
block
in css-display-3, for display,
in css-scroll-snap-1, for scroll-snap-type
in css2
in css2, for display
blue
bold
bolder
border-box
in css-backgrounds-3, for background-clip
in css-backgrounds-3, for background-origin
in css-masking-1, for mask-clip
in css-masking-1, for mask-origin
in css-shapes-1, for , shape-outside
in css-transforms-1, for transform-box
in css-ui-3, for box-sizing
both
in css-animations-1, for animation-fill-mode
in css-scroll-snap-1, for scroll-snap-type
in css2, for clear
bottom
in css-backgrounds-3, for background-position
in css-transforms-1, for transform-origin
in css2, for caption-side
in css2, for vertical-align
braille
in css2, for @media
in mediaqueries-4, for @media
break-all
break-spaces
break-word
in css-text-3, for overflow-wrap
in css-text-3, for word-break
bullets
cambodian
capitalize
caption
cell
center
in css-align-3, for ,
in css-align-3, for , , justify-self, align-self, justify-content, align-content
in css-backgrounds-3, for background-position
in css-flexbox-1, for align-content
in css-flexbox-1, for align-items, align-self
in css-flexbox-1, for justify-content
in css-scroll-snap-1, for scroll-snap-align
in css-speech-1, for voice-balance
in css-text-3, for text-align
in css-transforms-1, for transform-origin
ch
child
circle
in css-counter-styles-3, for
in css-images-3, for
in css-text-decor-3, for text-emphasis-style
in css-text-decor-3, for text-text-emphasis-style
in css2
in css2, for list-style-type
cjk-decimal
cjk-earthly-branch
cjk-heavenly-stem
cjk-ideographic
clip
clone
close-quote
in css2
in css2, for content
closest-corner
closest-side
cm
coarse
collapse
in css-display-3, for visibility
in css2, for border-collapse

in css-backgrounds-3, for box-shadow
in css-multicol-1, for column-rule-color
in css2, for border-color, border-top-color, border-right-color, border-bottom-color, border-left-color
color
color-burn
color-dodge
col-resize
column
in css-break-3, for break-before, break-after
in css-flexbox-1, for flex-direction
in css-grid-1, for grid-auto-flow
column-reverse
contain
in css-backgrounds-3, for background-size
in css-images-3, for object-fit
content
in css-contain-1, for contain
in css-flexbox-1, for flex-basis
content-box
in css-backgrounds-3, for background-clip
in css-backgrounds-3, for background-origin
in css-masking-1, for mask-clip
in css-masking-1, for mask-origin
in css-shapes-1, for , shape-outside
in css-transforms-1, for transform-box
in css-ui-3, for box-sizing
contents
in css-display-3, for display,
in css-will-change-1, for will-change
context-menu
copy


cover
in css-backgrounds-3, for background-size
in css-images-3, for object-fit
crisp-edges
crosshair
cursive

in css-grid-1, for
in css-will-change-1, for will-change
cyclic
darken
dashed
in css-backgrounds-3, for , border-style, border-top-style, border-left-style, border-bottom-style, border-right-style, border
in css2
in css2, for , border-top-style, border-right-style, border-bottom-style, border-left-style, border-style

decimal
in css-counter-styles-3, for
in css2
in css2, for list-style-type
decimal-leading-zero
in css-counter-styles-3, for
in css2
in css2, for list-style-type
default
deg
dense
devanagari
difference
digits
digits ?
disc
in css-counter-styles-3, for
in css2
in css2, for list-style-type
disclosure-closed
disclosure-open
distribute
dot
in css-text-decor-3, for text-emphasis-style
in css-text-decor-3, for text-text-emphasis-style
dotted
in css-backgrounds-3, for , border-style, border-top-style, border-left-style, border-bottom-style, border-right-style, border
in css2
in css2, for , border-top-style, border-right-style, border-bottom-style, border-left-style, border-style
double
in css-backgrounds-3, for , border-style, border-top-style, border-left-style, border-bottom-style, border-right-style, border
in css2
in css2, for , border-top-style, border-right-style, border-bottom-style, border-left-style, border-style
double-circle
in css-text-decor-3, for text-emphasis-style
in css-text-decor-3, for text-text-emphasis-style
dpcm
dpi
dppx
each-line
ease
ease-in
ease-in-out
ease-out
ellipse
ellipsis
em
embed
embossed
in css2, for @media
in mediaqueries-4, for @media
end
in css-align-3, for ,
in css-align-3, for , , justify-self, align-self, justify-content, align-content
in css-easing-1, for steps()
in css-scroll-snap-1, for scroll-snap-align
in css-text-3, for text-align

e-resize
ethiopic-numeric
evenodd
ew-resize
ex
exclude
exclusion
extends

fantasy
farthest-corner
farthest-side
fast
in css-speech-1, for voice-rate
in mediaqueries-4, for @media/update
female
fill
in css-backgrounds-3, for border-image-slice
in css-images-3, for object-fit
in css-masking-1, for mask-border-slice
fill-box
in css-masking-1, for clip-path
in css-masking-1, for mask-clip
in css-masking-1, for mask-origin
in css-transforms-1, for transform-box
filled
in css-text-decor-3, for text-emphasis-style
in css-text-decor-3, for text-text-emphasis-style
fine
first
in css-align-3, for justify-self, justify-items, align-content, align-self, align-items,
in css-text-3, for hanging-punctuation
first baseline
fit-content()
fixed
in css-backgrounds-3, for background-attachment
in css-counter-styles-3, for @counter-style/system
in css2, for position
in css2, for table-layout

flex
in css-display-3, for display,
in css-flexbox-1, for display
<'flex-basis'>
flex-end
in css-align-3, for ,
in css-align-3, for , , justify-self, align-self, justify-content, align-content
in css-flexbox-1, for align-content
in css-flexbox-1, for align-items, align-self
in css-flexbox-1, for justify-content
<'flex-grow'>
<'flex-shrink'>
flex-start
in css-align-3, for ,
in css-align-3, for , , justify-self, align-self, justify-content, align-content
in css-flexbox-1, for align-content
in css-flexbox-1, for align-items, align-self
in css-flexbox-1, for justify-content
flip
in css-images-3, for image-orientation
in css-images-3, for image-orientation
flow
flow-root
font-feature-settings
font-variant
in css-fonts-3
in css-fonts-3
force-end
forwards
fr

from-image
fr unit
fuchsia
full-size-kana
full-width
georgian
in css-counter-styles-3, for
in css2
in css2, for list-style-type
grab
grabbing
grad
gray
green
grid
in css-display-3, for display,
in css-grid-1, for display
<'grid-template-rows'> / [ auto-flow && dense? ] <'grid-auto-columns'>?
<'grid-template-rows'> / <'grid-template-columns'>
groove
in css-backgrounds-3, for , border-style, border-top-style, border-left-style, border-bottom-style, border-right-style, border
in css2
in css2, for , border-top-style, border-right-style, border-bottom-style, border-left-style, border-style
gujarati
gurmukhi
handheld
in css2, for @media
in mediaqueries-4, for @media
hanging
hard-light
hebrew
help
hidden
in css-backgrounds-3, for , border-style, border-top-style, border-left-style, border-bottom-style, border-right-style, border
in css-display-3, for visibility
in css2
in css2, for , border-top-style, border-right-style, border-bottom-style, border-left-style, border-style
in css2, for overflow
hide
high
in css-speech-1, for voice-pitch
in css-speech-1, for voice-range
high-quality
hiragana
hiragana-iroha
horizontal-tb
hover
hue
hz
icon

in
infinite
in css-animations-1, for animation-iteration-count
in mediaqueries-4, for @media/resolution
inherit
initial
inline
in css-display-3, for display,
in css-scroll-snap-1, for scroll-snap-type
in css2
in css2, for display
inline-block
in css-display-3, for display,
in css2
in css2, for display
inline-flex
in css-display-3, for display,
in css-flexbox-1, for display
inline-grid
in css-display-3, for display,
in css-grid-1, for display
inline-table
in css-display-3, for display,
in css2
in css2, for display
inset
in css-backgrounds-3, for , border-style, border-top-style, border-left-style, border-bottom-style, border-right-style, border
in css-backgrounds-3, for box-shadow
in css2
in css2, for , border-top-style, border-right-style, border-bottom-style, border-left-style, border-style
inside

in css-display-3, for order
in css-flexbox-1, for order
in css-speech-1, for voice-family

&& ?
inter-character
interlace
intersect
inter-word
invert
in css-ui-3, for outline-color
in css2
isolate
isolate-override
italic
japanese-formal
japanese-informal
jump-both
jump-end
jump-none
jump-start
justify
justify-all
kannada
katakana
katakana-iroha
keep-all

khmer
khz
korean-hangul-formal
korean-hanja-formal
korean-hanja-informal
landscape
lao
large
last
in css-align-3, for justify-self, justify-items, align-content, align-self, align-items,
in css-text-3, for hanging-punctuation
last baseline
layout
left
in css-align-3, for justify-content, justify-self, justify-items
in css-backgrounds-3, for background-position
in css-break-3, for break-before, break-after
in css-speech-1, for voice-balance
in css-text-3, for text-align
in css-text-decor-3, for text-emphasis-position
in css-text-decor-3, for text-text-emphasis-position
in css-text-decor-3, for text-underline-position
in css-transforms-1, for transform-origin
in css2, for clear
in css2, for float
in css2, for page-break-before, page-break-after, page-break-inside
leftwards
legacy

in css-backgrounds-3, for background-position
in css-images-3, for
in css-shapes-1, for shape-margin
in css-text-3, for letter-spacing
in css-text-3, for text-indent
in css-text-3, for word-spacing
in css2, for , border-top-width, border-right-width, border-bottom-wight, border-left-width, border-width
in css2, for
in css2, for top, right, bottom, left
in css2, for vertical-align


in css-grid-1, for grid-template-columns, grid-template-rows
in css-scroll-snap-1, for scroll-padding, scroll-padding-inline, scroll-padding-inline-start, scroll-padding-inline-end, scroll-padding-block, scroll-padding-block-start, scroll-padding-block-end
in css-shapes-1, for shape-margin

in css-backgrounds-3, for background-size
in css-backgrounds-3, for border-image-width
{2}
lighten
lighter
lime
linear
linearrgb
[ ? ? ? ]+ [ / ]?
line-through
in css-text-decor-3, for text-decoration-line
in css2, for text-decoration
list-item
in css-display-3, for display,
in css2
in css2, for display
literal-punctuation
local
loose
loud
low
in css-speech-1, for voice-pitch
in css-speech-1, for voice-range
lower-alpha
in css-counter-styles-3, for
in css2, for list-style-type
lower-armenian
lowercase
lower-greek
in css-counter-styles-3, for
in css2
in css2, for list-style-type
lower-latin
in css-counter-styles-3, for
in css2
in css2, for list-style-type
lower-roman
in css-counter-styles-3, for
in css2
in css2, for list-style-type
ltr
luminance
in css-masking-1, for mask-border-mode
in css-masking-1, for mask-mode
in css-masking-1, for mask-type
luminosity
malayalam
male
mandatory
manual
margin-box
maroon
match-parent
match-source
max-content
medium
in css-backgrounds-3, for , border-width, border-top-width, border-left-width, border-bottom-width, border-right-width, border
in css-speech-1, for pause-before, pause-after
in css-speech-1, for rest-before, rest-after
in css-speech-1, for voice-pitch
in css-speech-1, for voice-range
in css-speech-1, for voice-rate
in css-speech-1, for voice-volume
in css2, for , border-top-width, border-right-width, border-bottom-wight, border-left-width, border-width
in css2, for font-size
message-box
middle
min-content
minmax()
mixed
mm
moderate
mongolian
monospace
move
ms
multiply
myanmar
navy
ne-resize
nesw-resize
neutral
never
no-clip
no-close-quote
in css2
in css2, for content
no-drop
none
in css-animations-1, for animation-fill-mode
in css-animations-1, for animation-name
in css-backgrounds-3, for , border-style, border-top-style, border-left-style, border-bottom-style, border-right-style, border
in css-backgrounds-3, for background-image
in css-backgrounds-3, for box-shadow
in css-contain-1, for contain
in css-display-3, for display,
in css-flexbox-1, for flex
in css-grid-1, for grid-template
in css-grid-1, for grid-template-areas
in css-grid-1, for grid-template-rows, grid-template-columns
in css-images-3, for image-orientation
in css-images-3, for object-fit
in css-multicol-1, for column-span
in css-scroll-snap-1, for scroll-snap-align
in css-scroll-snap-1, for scroll-snap-type
in css-shapes-1, for shape-outside
in css-speech-1, for pause-before, pause-after
in css-speech-1, for rest-before, rest-after
in css-speech-1, for voice-stress
in css-text-3, for hanging-punctuation
in css-text-3, for hyphens
in css-text-3, for text-justify
in css-text-3, for text-transform
in css-text-decor-3, for text-decoration-line
in css-text-decor-3, for text-emphasis-style
in css-text-decor-3, for text-text-emphasis-style
in css-transitions-1, for transition-property
in css-ui-3, for cursor
in css-writing-modes-4, for text-combine-upright
in css2
in css2, for , border-top-style, border-right-style, border-bottom-style, border-left-style, border-style
in css2, for clear
in css2, for content
in css2, for counter-reset, counter-increment
in css2, for display
in css2, for float
in css2, for list-style-type
in css2, for max-height
in css2, for max-width
in css2, for quotes
in css2, for text-decoration
in mediaqueries-4, for @media/hover
in mediaqueries-4, for @media/overflow-block
in mediaqueries-4, for @media/overflow-inline
in mediaqueries-4, for @media/pointer
in mediaqueries-4, for @media/update
none!!font-variant
nonzero
no-open-quote
in css2
in css2, for content
no-punctuation
no-repeat
normal
in compositing-1, for
in css-align-3, for align-self
in css-align-3, for justify-content, align-content
in css-align-3, for justify-self
in css-align-3, for row-gap, column-gap, gap
in css-animations-1, for animation-direction
in css-scroll-snap-1, for scroll-snap-stop
in css-speech-1, for speak-as
in css-speech-1, for voice-rate
in css-speech-1, for voice-stress
in css-text-3, for letter-spacing
in css-text-3, for line-break
in css-text-3, for overflow-wrap
in css-text-3, for white-space
in css-text-3, for word-break
in css-text-3, for word-spacing
in css-writing-modes-4, for unicode-bidi
in css2, for content
in css2, for font-style
in css2, for font-variant
in css2, for font-weight
in css2, for line-height
normal!!font-feature-settings
normal!!font-variant
not
not-allowed
nowrap
in css-flexbox-1, for flex-wrap
in css-text-3, for white-space
n-resize
ns-resize

in css-animations-1, for animation-iteration-count
in css-flexbox-1, for flex-grow
in css-flexbox-1, for flex-shrink
in css-fonts-3, for font-size-adjust
in css-shapes-1, for shape-image-threshold
in css-speech-1, for voice-balance

in css-backgrounds-3, for border-image-slice
in css-backgrounds-3, for border-image-width
numbers
numeric
nw-resize
nwse-resize
objectboundingbox
in css-masking-1, for clipPathUnits
in css-masking-1, for maskContentUnits
in css-masking-1, for maskUnits
oblique
old
olive
only
open
open-quote
in css2
in css2, for content
orange
oriya
outset
in css-backgrounds-3, for , border-style, border-top-style, border-left-style, border-bottom-style, border-right-style, border
in css2
in css2, for , border-top-style, border-right-style, border-bottom-style, border-left-style, border-style
outside
over
in css-text-decor-3, for text-emphasis-position
in css-text-decor-3, for text-text-emphasis-position
overlay
overline
in css-text-decor-3, for text-decoration-line
in css2, for text-decoration
p3
padding-box
in css-backgrounds-3, for background-clip
in css-backgrounds-3, for background-origin
in css-masking-1, for mask-clip
in css-masking-1, for mask-origin
in css-shapes-1, for , shape-outside
page
paged
paint
paused
pc

in css-backgrounds-3, for background-position
in css-shapes-1, for shape-margin
in css-speech-1, for voice-pitch
in css-speech-1, for voice-range
in css-speech-1, for voice-rate
in css-text-3, for text-indent
in css2, for
in css2, for top, right, bottom, left
in css2, for vertical-align

persian
pixelated
pixel unit
plaintext
pointer
portrait

pre
pre-line
preserve
pre-wrap
in css2, for @media
in mediaqueries-4, for @media
progress
progressive
projection
in css2, for @media
in mediaqueries-4, for @media
proximity
pt
purple
px
rad
rec2020
recto
red
reduced
region
relative
rem
repeat
in css-backgrounds-3, for background-repeat
in css-backgrounds-3, for border-image-repeat
repeat-x
repeat-y
reverse
revert
ridge
in css-backgrounds-3, for , border-style, border-top-style, border-left-style, border-bottom-style, border-right-style, border
in css2
in css2, for , border-top-style, border-right-style, border-bottom-style, border-left-style, border-style
right
in css-align-3, for justify-content, justify-self, justify-items
in css-backgrounds-3, for background-position
in css-break-3, for break-before, break-after
in css-speech-1, for voice-balance
in css-text-3, for text-align
in css-text-decor-3, for text-emphasis-position
in css-text-decor-3, for text-text-emphasis-position
in css-text-decor-3, for text-underline-position
in css-transforms-1, for transform-origin
in css2, for clear
in css2, for float
in css2, for page-break-before, page-break-after, page-break-inside
rightwards
round
in css-backgrounds-3, for background-repeat
in css-backgrounds-3, for border-image-repeat
row
in css-flexbox-1, for flex-direction
in css-grid-1, for grid-auto-flow
row-resize
row-reverse
rtl
ruby
ruby-base
ruby-base-container
ruby-text
ruby-text-container
run-in
running
safe
sans-serif
saturation
scale-down
screen
in compositing-1, for
in css2, for @media
in mediaqueries-4, for @media
scroll
in css-backgrounds-3, for background-attachment
in css2, for overflow
in mediaqueries-4, for @media/overflow-block
in mediaqueries-4, for @media/overflow-inline
scroll-position
self-end
in css-align-3, for
in css-align-3, for , justify-self, align-self
self-start
in css-align-3, for
in css-align-3, for , justify-self, align-self

in css-speech-1, for voice-pitch
in css-speech-1, for voice-range
separate
se-resize
serif
sesame
in css-text-decor-3, for text-emphasis-style
in css-text-decor-3, for text-text-emphasis-style
show
sideways
sideways-lr
sideways-right
sideways-rl
silent
silver
simp-chinese-formal
simp-chinese-informal

size
slice
slow
in css-speech-1, for voice-rate
in mediaqueries-4, for @media/update
small
small-caps
small-caption
smooth
soft
soft-light
solid
in css-backgrounds-3, for , border-style, border-top-style, border-left-style, border-bottom-style, border-right-style, border
in css2
in css2, for , border-top-style, border-right-style, border-bottom-style, border-left-style, border-style
space
in css-backgrounds-3, for background-repeat
in css-backgrounds-3, for border-image-repeat
space-around
in css-align-3, for align-content, justify-content,
in css-flexbox-1, for align-content
in css-flexbox-1, for justify-content
space-between
in css-align-3, for align-content, justify-content,
in css-flexbox-1, for align-content
in css-flexbox-1, for justify-content
space-evenly
span && [ || ]
speech
in css2, for @media
in mediaqueries-4, for @media
spell-out
in css-counter-styles-3, for @counter-style/speak-as
in css-speech-1, for speak-as
square
in css-counter-styles-3, for
in css2
in css2, for list-style-type
s-resize
srgb
in filter-effects-1, for color-interpolation-filters
in mediaqueries-4, for @media/color-gamut
start
in css-align-3, for ,
in css-align-3, for , , justify-self, align-self, justify-content, align-content
in css-easing-1, for steps()
in css-scroll-snap-1, for scroll-snap-align
in css-text-3, for text-align
static
status-bar
step-end
step-start
stretch
in css-align-3, for align-content, justify-content,
in css-align-3, for align-self
in css-align-3, for justify-self
in css-backgrounds-3, for border-image-repeat
in css-flexbox-1, for align-content
in css-flexbox-1, for align-items, align-self
strict
in css-contain-1, for contain
in css-text-3, for line-break

in css-shapes-1, for path()
in css-text-decor-3, for text-emphasis-style
in css-text-decor-3, for text-text-emphasis-style
in css2, for content
+
[ ]+
stroke-box
in css-masking-1, for clip-path
in css-masking-1, for mask-clip
in css-masking-1, for mask-origin
in css-transforms-1, for transform-box
strong
in css-speech-1, for pause-before, pause-after
in css-speech-1, for rest-before, rest-after
in css-speech-1, for voice-stress
sub
subtract
super
sw-resize
symbolic
table
in css-display-3, for display,
in css2
in css2, for display
table-caption
in css-display-3, for display,
in css2
in css2, for display
table-cell
in css-display-3, for display,
in css2
in css2, for display
table-column
in css-display-3, for display,
in css2
in css2, for display
table-column-group
in css-display-3, for display,
in css2
in css2, for display
table-footer-group
in css-display-3, for display,
in css2
in css2, for display
table-header-group
in css-display-3, for display,
in css2
in css2, for display
table-row
in css-display-3, for display,
in css2
in css2, for display
table-row-group
in css-display-3, for display,
in css2
in css2, for display
tamil
teal
telugu
text
text-bottom
text-top
thai
thick
in css-backgrounds-3, for , border-width, border-top-width, border-left-width, border-bottom-width, border-right-width, border
in css2, for , border-top-width, border-right-width, border-bottom-wight, border-left-width, border-width
thin
in css-backgrounds-3, for , border-width, border-top-width, border-left-width, border-bottom-width, border-right-width, border
in css2, for , border-top-width, border-right-width, border-bottom-wight, border-left-width, border-width
tibetan

in css-animations-1, for animation-delay
in css-animations-1, for animation-duration
in css-speech-1, for pause-before, pause-after
in css-speech-1, for rest-before, rest-after
in css-speech-1, for voice-duration
top
in css-backgrounds-3, for background-position
in css-transforms-1, for transform-origin
in css2, for caption-side
in css2, for vertical-align
|
trad-chinese-formal
trad-chinese-informal
transparent
triangle
in css-text-decor-3, for text-emphasis-style
in css-text-decor-3, for text-text-emphasis-style
tty
in css2, for @media
in mediaqueries-4, for @media
turn
tv
in css2, for @media
in mediaqueries-4, for @media
under
in css-text-decor-3, for text-emphasis-position
in css-text-decor-3, for text-text-emphasis-position
in css-text-decor-3, for text-underline-position
underline
in css-text-decor-3, for text-decoration-line
in css2, for text-decoration
unsafe
unset
upper-alpha
in css-counter-styles-3, for
in css2, for list-style-type
upper-armenian
uppercase
upper-latin
in css-counter-styles-3, for
in css2
in css2, for list-style-type
upper-roman
in css-counter-styles-3, for
in css2
in css2, for list-style-type
upright


in css-speech-1, for cue-before, cue-after
in css2, for background-image
in css2, for content

userspaceonuse
in css-masking-1, for clipPathUnits
in css-masking-1, for maskContentUnits
in css-masking-1, for maskUnits
verso
vertical-lr
vertical-rl
vertical-text
vh
view-box
in css-masking-1, for clip-path
in css-masking-1, for mask-clip
in css-masking-1, for mask-origin
in css-transforms-1, for transform-box
visible
in css-display-3, for visibility
in css2, for overflow
vmax
vmin
vw
wait
weak
in css-speech-1, for pause-before, pause-after
in css-speech-1, for rest-before, rest-after
white
words
wrap
wrap-reverse
w-resize
x-fast
x-high
in css-speech-1, for voice-pitch
in css-speech-1, for voice-range
x-large
x-loud
x-low
in css-speech-1, for voice-pitch
in css-speech-1, for voice-range
x-slow
x-small
x-soft
x-strong
in css-speech-1, for pause-before, pause-after
in css-speech-1, for rest-before, rest-after
x-weak
in css-speech-1, for pause-before, pause-after
in css-speech-1, for rest-before, rest-after
xx-large
xx-small
yellow
young
zoom-in
zoom-out
6.
Acknowledgements
Special thanks to Florian Rivoal for creating the initial draft of the
§ 3.2.1 Experimentation and Unstable Features
recommendations.
Conformance
Document conventions
Conformance requirements are expressed with a combination of
descriptive assertions and RFC 2119 terminology. The key words “MUST”,
“MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”,
“RECOMMENDED”, “MAY”, and “OPTIONAL” in the normative parts of this
document are to be interpreted as described in RFC 2119.
However, for readability, these words do not appear in all uppercase
letters in this specification.
All of the text of this specification is normative except sections
explicitly marked as non-normative, examples, and notes.
[RFC2119]
Examples in this specification are introduced with the words “for example”
or are set apart from the normative text with
class="example"
like this:
This is an example of an informative example.
Informative notes begin with the word “Note” and are set apart from the
normative text with
class="note"
, like this:
Note, this is an informative note.
Advisements are normative sections styled to evoke special attention and are
set apart from other normative text with

, like
this:
UAs MUST provide an accessible alternative.
Conformance classes
Conformance to this specification
is defined for three conformance classes:
style sheet
CSS
style sheet
renderer
UA
that interprets the semantics of a style sheet and renders
documents that use them.
authoring tool
UA
that writes a style sheet.
A style sheet is conformant to this specification
if all of its statements that use syntax defined in this module are valid
according to the generic CSS grammar and the individual grammars of each
feature defined in this module.
A renderer is conformant to this specification
if, in addition to interpreting the style sheet as defined by the
appropriate specifications, it supports all the features defined
by this specification by parsing them correctly
and rendering the document accordingly. However, the inability of a
UA to correctly render a document due to limitations of the device
does not make the UA non-conformant. (For example, a UA is not
required to render color on a monochrome monitor.)
An authoring tool is conformant to this specification
if it writes style sheets that are syntactically correct according to the
generic CSS grammar and the individual grammars of each feature in
this module, and meet all other conformance requirements of style sheets
as described in this module.
Partial implementations
So that authors can exploit the forward-compatible parsing rules to
assign fallback values, CSS renderers
must
treat as invalid (and
ignore
as appropriate
) any at-rules, properties, property values, keywords,
and other syntactic constructs for which they have no usable level of
support. In particular, user agents
must not
selectively
ignore unsupported component values and honor supported values in a single
multi-value property declaration: if any value is considered invalid
(as unsupported values must be), CSS requires that the entire declaration
be ignored.
Implementations of Unstable and Proprietary Features
To avoid clashes with future stable CSS features,
the CSSWG recommends
following best practices
for the implementation of
unstable
features and
proprietary extensions
to CSS.
Non-experimental implementations
Once a specification reaches the Candidate Recommendation stage,
non-experimental implementations are possible, and implementors should
release an unprefixed implementation of any CR-level feature they
can demonstrate to be correctly implemented according to spec.
To establish and maintain the interoperability of CSS across
implementations, the CSS Working Group requests that non-experimental
CSS renderers submit an implementation report (and, if necessary, the
testcases used for that implementation report) to the W3C before
releasing an unprefixed implementation of any CSS features. Testcases
submitted to W3C are subject to review and correction by the CSS
Working Group.
Further information on submitting testcases and implementation reports
can be found from on the CSS Working Group’s website at
Questions should be directed to the
public-css-testsuite@w3.org
mailing list.
References
Normative References
[COMPOSITING]
Rik Cabanier; Nikos Andronikos.
Compositing and Blending Level 1
. 13 January 2015. CR. URL:
[CSS-BACKGROUNDS-3]
Bert Bos; Elika Etemad; Brad Kemper.
CSS Backgrounds and Borders Module Level 3
. 26 July 2021. CR. URL:
[CSS-BOX-3]
Elika Etemad.
CSS Box Model Module Level 3
. 22 December 2020. CR. URL:
[CSS-CASCADE-4]
Elika Etemad; Tab Atkins Jr..
CSS Cascading and Inheritance Level 4
. 3 December 2021. WD. URL:
[CSS-COLOR-3]
Tantek Çelik; Chris Lilley; David Baron.
CSS Color Module Level 3
. 5 August 2021. REC. URL:
[CSS-COLOR-4]
Tab Atkins Jr.; Chris Lilley; Lea Verou.
CSS Color Module Level 4
. 15 December 2021. WD. URL:
[CSS-CONDITIONAL-3]
David Baron; Elika Etemad; Chris Lilley.
CSS Conditional Rules Module Level 3
. 8 December 2020. CR. URL:
[CSS-CONTAIN-1]
Tab Atkins Jr.; Florian Rivoal.
CSS Containment Module Level 1
. 22 December 2020. REC. URL:
[CSS-COUNTER-STYLES-3]
Tab Atkins Jr..
CSS Counter Styles Level 3
. 27 July 2021. CR. URL:
[CSS-DISPLAY-3]
Tab Atkins Jr.; Elika Etemad.
CSS Display Module Level 3
. 3 September 2021. CR. URL:
[CSS-EASING-1]
Brian Birtles; et al.
CSS Easing Functions Level 1
. 1 April 2021. CR. URL:
[CSS-FLEXBOX-1]
Tab Atkins Jr.; et al.
CSS Flexible Box Layout Module Level 1
. 19 November 2018. CR. URL:
[CSS-FONTS-3]
John Daggett; Myles Maxfield; Chris Lilley.
CSS Fonts Module Level 3
. 20 September 2018. REC. URL:
[CSS-FONTS-4]
John Daggett; Myles Maxfield; Chris Lilley.
CSS Fonts Module Level 4
. 29 July 2021. WD. URL:
[CSS-GRID-1]
Tab Atkins Jr.; et al.
CSS Grid Layout Module Level 1
. 18 December 2020. CR. URL:
[CSS-GRID-2]
Tab Atkins Jr.; Elika Etemad; Rossen Atanassov.
CSS Grid Layout Module Level 2
. 18 December 2020. CR. URL:
[CSS-IMAGES-3]
Tab Atkins Jr.; Elika Etemad; Lea Verou.
CSS Images Module Level 3
. 17 December 2020. CR. URL:
[CSS-IMAGES-4]
Tab Atkins Jr.; Elika Etemad; Lea Verou.
CSS Image Values and Replaced Content Module Level 4
. 13 April 2017. WD. URL:
[CSS-LISTS-3]
Elika Etemad; Tab Atkins Jr..
CSS Lists and Counters Module Level 3
. 17 November 2020. WD. URL:
[CSS-LOGICAL-1]
Rossen Atanassov; Elika Etemad.
CSS Logical Properties and Values Level 1
. 27 August 2018. WD. URL:
[CSS-MULTICOL-1]
Florian Rivoal; Rachel Andrew.
CSS Multi-column Layout Module Level 1
. 12 October 2021. CR. URL:
[CSS-POSITION-3]
Elika Etemad; Tab Atkins Jr..
CSS Positioned Layout Module Level 3
. 16 December 2021. WD. URL:
[CSS-SIZING-3]
Tab Atkins Jr.; Elika Etemad.
CSS Box Sizing Module Level 3
. 17 December 2021. WD. URL:
[CSS-SIZING-4]
Tab Atkins Jr.; Elika Etemad; Jen Simmons.
CSS Box Sizing Module Level 4
. 20 May 2021. WD. URL:
[CSS-STYLE-ATTR]
Tantek Çelik; Elika Etemad.
CSS Style Attributes
. 7 November 2013. REC. URL:
[CSS-SYNTAX-3]
Tab Atkins Jr.; Simon Sapin.
CSS Syntax Module Level 3
. 16 July 2019. CR. URL:
[CSS-TRANSFORMS-1]
Simon Fraser; et al.
CSS Transforms Module Level 1
. 14 February 2019. CR. URL:
[CSS-TRANSFORMS-2]
Tab Atkins Jr.; et al.
CSS Transforms Module Level 2
. 9 November 2021. WD. URL:
[CSS-UI-3]
Tantek Çelik; Florian Rivoal.
CSS Basic User Interface Module Level 3 (CSS3 UI)
. 21 June 2018. REC. URL:
[CSS-VALUES-3]
Tab Atkins Jr.; Elika Etemad.
CSS Values and Units Module Level 3
. 6 June 2019. CR. URL:
[CSS-VARIABLES-1]
Tab Atkins Jr..
CSS Custom Properties for Cascading Variables Module Level 1
. 11 November 2021. CR. URL:
[CSS-WILL-CHANGE-1]
Tab Atkins Jr..
CSS Will Change Module Level 1
. 3 December 2015. CR. URL:
[CSS-WRITING-MODES-3]
Elika Etemad; Koji Ishii.
CSS Writing Modes Level 3
. 10 December 2019. REC. URL:
[CSS2]
Bert Bos; et al.
Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification
. 7 June 2011. REC. URL:
[CSS3-MEDIAQUERIES]
Florian Rivoal; et al.
Media Queries
. 19 June 2012. REC. URL:
[CSS3-NAMESPACE]
Elika Etemad.
CSS Namespaces Module Level 3
. 20 March 2014. REC. URL:
[RESIZE-OBSERVER-1]
Aleks Totic; Greg Whitworth.
Resize Observer
. 11 February 2020. WD. URL:
[RFC2119]
S. Bradner.
Key words for use in RFCs to Indicate Requirement Levels
. March 1997. Best Current Practice. URL:
[SELECTORS-3]
Tantek Çelik; et al.
Selectors Level 3
. 6 November 2018. REC. URL:
[SELECTORS-4]
Elika Etemad; Tab Atkins Jr..
Selectors Level 4
. 21 November 2018. WD. URL:
[WEB-ANIMATIONS-1]
Brian Birtles; et al.
Web Animations
. 18 May 2021. WD. URL:
Informative References
[CSS-ALIGN-3]
Elika Etemad; Tab Atkins Jr..
CSS Box Alignment Module Level 3
. 21 April 2020. WD. URL:
[CSS-ANIMATIONS-1]
Dean Jackson; et al.
CSS Animations Level 1
. 11 October 2018. WD. URL:
[CSS-BREAK-3]
Rossen Atanassov; Elika Etemad.
CSS Fragmentation Module Level 3
. 4 December 2018. CR. URL:
[CSS-CASCADE-3]
Elika Etemad; Tab Atkins Jr..
CSS Cascading and Inheritance Level 3
. 11 February 2021. REC. URL:
[CSS-FONT-LOADING-3]
Tab Atkins Jr..
CSS Font Loading Module Level 3
. 22 May 2014. WD. URL:
[CSS-MASKING-1]
Dirk Schulze; Brian Birtles; Tab Atkins Jr..
CSS Masking Module Level 1
. 5 August 2021. CR. URL:
[CSS-SCROLL-SNAP-1]
Matt Rakow; et al.
CSS Scroll Snap Module Level 1
. 11 March 2021. CR. URL:
[CSS-SCROLLBARS-1]
Tantek Çelik; Rossen Atanassov; Florian Rivoal.
CSS Scrollbars Styling Module Level 1
. 9 December 2021. CR. URL:
[CSS-SHAPES-1]
Vincent Hardy; Rossen Atanassov; Alan Stearns.
CSS Shapes Module Level 1
. 20 March 2014. CR. URL:
[CSS-SPEECH-1]
Daniel Weck.
CSS Speech Module
. 10 March 2020. CR. URL:
[CSS-TEXT-3]
Elika Etemad; Koji Ishii; Florian Rivoal.
CSS Text Module Level 3
. 22 April 2021. CR. URL:
[CSS-TEXT-DECOR-3]
Elika Etemad; Koji Ishii.
CSS Text Decoration Module Level 3
. 13 August 2019. CR. URL:
[CSS-TRANSITIONS-1]
David Baron; et al.
CSS Transitions
. 11 October 2018. WD. URL:
[CSS-WRITING-MODES-4]
Elika Etemad; Koji Ishii.
CSS Writing Modes Level 4
. 30 July 2019. CR. URL:
[FILTER-EFFECTS-1]
Dirk Schulze; Dean Jackson.
Filter Effects Module Level 1
. 18 December 2018. WD. URL:
[MEDIAQUERIES-4]
Florian Rivoal; Tab Atkins Jr..
Media Queries Level 4
. 21 July 2020. CR. URL:
#editors-draft
Referenced in:
1.1.
Background: The W3C Process and CSS
(2)
#css-level-1
Referenced in:
2.4.
CSS Levels
#css-level-2
Referenced in:
2.4.
CSS Levels
(2)
(3)
#css-level-3
Referenced in:
2.4.
CSS Levels
#unstable
Referenced in:
3.2. Implementations of Unstable and Proprietary Features
3.2.1.
Experimentation and Unstable Features
(2)
3.2.3.
Market Pressure and De Facto Standards
(2)
3.2.3.1.
Vendor-prefixing Unstable Features
(2)
#vendor-prefix
Referenced in:
3.2.2.
Proprietary and Non-standardized Features
3.2.3.
Market Pressure and De Facto Standards
3.2.3.1.
Vendor-prefixing Unstable Features
(2)
(3)
3.3. Implementations of CR-level Features
#proprietary-extension
Referenced in:
3.2. Implementations of Unstable and Proprietary Features
3.2.2.
Proprietary and Non-standardized Features
(2)
(3)
#rough-interoperability
Referenced in:
2.3.
Modules with Rough Interoperability
3.2.3.
Market Pressure and De Facto Standards