CSS Snapshot 2021
CSS Snapshot 2021
Editor’s Draft
29 January 2025
More details about this document
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Latest published version:
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Feedback:
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Editors:
Tab Atkins Jr.
Google
Elika J. Etemad / fantasai
Apple
Florian Rivoal
Invited Expert
Suggest an Edit for this Spec:
GitHub Editor
World Wide Web Consortium
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 is a public copy of the editors’ draft.
It is provided for discussion only and may change at any moment.
Its publication here does not imply endorsement of its contents by W3C.
Don’t cite this document other than as work in progress.
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
18 August 2025 W3C Process Document
This document represents the state of CSS as of 2021.
The CSS Working Group does not expect any further changes to this document:
new snapshots will be published at
as CSS advances.
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.
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
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.
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.
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.
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 §16.3,
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 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.
CSS Color Adjustment Module Level 1
[CSS-COLOR-ADJUST-1]
This module introduces a model and controls over automatic color adjustment by the user agent to handle user preferences and device output optimizations.
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
translate
rotate
, and
scale
properties.
[CSS-TRANSFORMS-2]
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
in css2
in css2
~=
1st
2d matrix
2nd
3rd
4th
absolute length
absolute length unit
absolutely positioned element
absolute scroll
abstract dimensions
:active
activeborder
activecaption
active duration
active (pseudo-class)
actual value
actual values
additive tuple
adjoining
adjoining margins
adjusted radius dimension
advance measure
:after
in css2
in css2
after
after-change style
aliceblue
aligned subtree
alignment baseline
alignment container
alignment context
alignment subject
'all' media group
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
aquamarine
are a valid escape
at-keyword
atomic inline
atomic inline box
atomic inline-level box
atomic inline-level boxes
at-rule
at-rules
attr()
attribute
'audio' media group
auditory icon
augmented grid
aural box model
author
authoring tool
author origin
author-origin
author presentational hint origin
author style sheet
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 color
background image
background image layer
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
in css2
in css2
before
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
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 element
block-level elements
block scripts
block size
block-size
block start
block-start
blue
blueviolet
blur radius
boolean context
border
border box
border color
border edge
border image
border image area
border image region
border (of a box)
border::of a box
border radius
border style
border width
bottom
box
box alignment properties
box::border
box::content
box::content height
box::content width
box-corner
box fragment
box::margin
box::overflow
box::padding
box tree
break
brown
burlywood
buttonface
buttonhighlight
buttonshadow
buttontext
cadetblue
cancel
canonical unit
canvas
canvas background
canvas surface
captiontext
captures snap positions
cascade
cascade-dependent keyword
cascaded value
cascade origin
central baseline
character
character encoding
"@charset"
chartreuse
check if three code points would start an ident sequence
check if three code points would start a number
check if three code points would start a unicode-range
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
clustered scripts
collapse
collapsed
collapsed flex item
collapsed grid track
collapsed gutter
collapsed margin
collapse through
collapsible white space
collapsing margin
color
color stop
color stop list
color transition hint
column box
column break
column gap
column height
column rule
column width
combinator
combinators
in css2
in selectors-3
combined duration
comments
compatible baseline alignment preferences
compatible units
complete
completed transition
component value
computed
computed repeat notation
computed track list
computed track size
computed value
computed values
concrete object size
conditional group rule
conditional import
conditionally hang
conformance
consecutive
constraint rectangle
consume a block
consume a block's contents
consume a component value
consume a declaration
consume a function
consume a list of component values
consume a list of declarations
consume a list of rules
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 stylesheet's contents
consume a token
in css-syntax-3
in css-syntax-3, for token stream
in css-syntax-3, for tokenizer
consume a unicode-range token
consume a url token
consume comments
consume the next input token
consume the remnants of a bad declaration
consume the remnants of a bad url
consume the value of a unicode-range descriptor
contain constraint
containing block
containing block chain
containing block for all descendants
containing block::initial
containment
content
content area
content-based minimum size
in css-flexbox-1
in css-grid-1
content box
content distribution
content-distribution
content-distribution properties
content edge
content height
content language
content (of a box)
content::of a box
content::rendered
content size suggestion
in css-flexbox-1
in css-grid-1
content width
content writing system
continuous media
'continuous' media group
convert a string to a number
coordinated self-alignment preference
coral
cornflowerblue
cornsilk
counter()
counters
counter style
counter symbol
cover constraint
crimson
cross axis
cross-axis
cross-axis baseline set
cross dimension
cross-end
cross size
cross size property
cross-start
css bracketed range notation
css-connected
css feature queries
css ident
css identifier
css ident sequence
css qualified name
css value definition syntax
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 bytes
decorating box
deeppink
deepskyblue
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 declarations
destination
determine the fallback encoding
device pixel
dice
digit
dimension
dimgray
dimgrey
direction-agnostic size
directional embedding
directional override
discard a mark
discard a token
discard whitespace
display type
distributed alignment
distribute extra space
document
document language
document order
document tree
document white space
document white space characters
dodgerblue
dominant baseline
easing function
east asian width property
element
in css-display-3, for CSS
in css2
element::following
element::preceding
element tree
empty
in css-syntax-3, for token stream
in css2
em (unit)
encapsulation contexts
end
ending point
ending shape
ending token
endmost
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 name
explicit grid
explicit grid column
explicit grid properties
explicit grid row
explicit grid track
explicitly-assigned line name
ex (unit)
fallback alignment
false in the negative range
fantasy
fetch an @import
fictional tag sequence
filter code points
filtered code points
filter function
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
first-baseline alignment
first-baseline content-alignment
first baselines
first-baseline self-alignment
first baseline set
:first-child
first-child
first cross-axis baseline set
first formatted line
:first-letter
first-letter
:first-line
first-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
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
focus
focus (pseudo-class)
following element
font-relative lengths
font source
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
fuchsia
full-size
full-size kana
full-width
fully inflexible
function
functional notation
gainsboro
general category
generate a counter
generate a counter representation
generate baselines
generated content
ghostwhite
go
gold
goldenrod
gradient-average-color
gradient box
gradient center
gradient function
gradient line
grapheme cluster
gray
graytext
green
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 layout algorithm
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
honeydew
horizontal axis
horizontal-axis
horizontal block flow
horizontal dimension
horizontal offset
horizontal-only
horizontal script
horizontal typographic mode
horizontal writing mode
hotpink
:hover
hover (pseudo-class)
hyphenate
hyphenation
hyphenation opportunity
hyphen-separated matching
hypothetical cross size
hypothetical fr size
hypothetical main size
ident
ident code point
identifier
in css-values-3, for CSS
in css2
identity transform
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
@import
important
import conditions
inactiveborder
inactivecaption
inactivecaptiontext
indefinite
indefinite size
independent formatting context
index
indianred
indigo
infinitely growable
in flow
in-flow
infobackground
infotext
inherit
in css-cascade-4
in css-cascade-4, for CSS
inheritance
in css-cascade-4
in css-cascade-4, for CSS
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
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 element
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
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
intrinsic dimensions
intrinsic sizing function
invalid
invalid at computed-value time
invalid image
invalid rule error
invisible
invisible box
isolated sequence
isolation
iteration order
ivory
japanese
justification opportunity
keyword
khaki
known
korean
:lang
lang (pseudo-class)
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
left
leftover space
legacy name alias
legacy shorthand
legacy value alias
lemonchiffon
letter
in css-syntax-3
in css-text-3
lightblue
lightcoral
lightcyan
lightgoldenrodyellow
lightgray
lightgreen
lightgrey
lightpink
lightsalmon
lightseagreen
lightskyblue
lightslategray
lightslategrey
light source
lightsteelblue
lightyellow
lime
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
:link
link (pseudo-class)
list-item
list properties
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 property
main-start
map document language elements to table elements
margin
margin box
margin edge
margin (of a box)
margin::of a box
mark
marked indexes
maroon
mask border image
mask border image area
mask image
mask layer image
mask painting area
mask-position
mask positioning area
mask-size
match
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
media condition
media-dependent import
media feature
media group
media groups
media query
media query list
media query modifier
media type
mediumaquamarine
mediumblue
mediumorchid
mediumpurple
mediumseagreen
mediumslateblue
mediumspringgreen
mediumturquoise
mediumvioletred
menutext
message entity
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-column spanner
multi-column spanning element
multi-line flex container
multiple declarations
multiply
must
must not
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
nearest neighbor
newline
next input code point
next input token
next-sibling combinator
next token
non-ascii code point
non-ascii ident code point
'none'::as display value
non-overridable counter-style names
non-printable code point
non-replaced
non-replaced element
normal
normalize into a token stream
null cell token
number
numeric data types
objects
object size negotiation
occupied
oldlace
olive
olivedrab
opacity
operating coordinate space
optimal viewing region
optional
orange
orangered
orchid
order-modified document order
orthogonal
orthogonal flow
other space separators
outer box-shadow
outer display type
outer edge
outline
out of flow
out-of-flow
output of the cascade
output progress value
outset-adjusted border radius
over
overflow
overflow alignment
overflow columns
padding
padding box
padding edge
padding (of a box)
padding::of a box
@page
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 block's contents
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
parse a stylesheet's contents
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
peru
physical
physical bottom
physical dimensions
physical direction
physical left
physical right
physical top
physical unit
pink
pixel
pixel unit
plum
positional alignment
positioned
positioned element/box
positioning scheme
positioning schemes:
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
process
propagate
propagation
proper table child
proper table row parent
property
in css-cascade-4, for CSS
in css2
property declarations
pseudo-classes
pseudo-classes:::active
pseudo-classes:::focus
pseudo-classes:::hover
pseudo-classes:::lang
pseudo-classes:::link
pseudo-classes:::visited
pseudo-class:::first
pseudo-class:::left
pseudo-class:::right
pseudo-elements
pseudo-elements:::after
in css2
in css2
pseudo-elements:::before
in css2
in css2
pseudo-elements:::first-letter
pseudo-elements:::first-line
purple
quad width
qualified rule
range context
recommended
reconsume the current input code point
reconsume the current input token
red
reference box
in css-shapes-1, for
in css-transforms-1
reference pixel
region break
relative length
relative length unit
relative positioning
relative scroll
relative units
remaining fragmentainer extent
remaining free space
rendered content
replaced
replaced element
representation
required
reset-only sub-property
re-snap
resolved type
restore a mark
reversing-adjusted start value
reversing shortening factor
:right
right
root
root element
rosybrown
row group box
row groups
royalblue
rule
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::match
selector matches
selector::subject of
self-alignment
self-alignment properties
semitone
separated borders model
sequence of simple selectors
serialize an
serif
set entries
shall
shall not
shared alignment context
sheet
sheets
shorthand
shorthand properties
shorthand property
should
should not
sibling
sideways typesetting
sienna
silver
simple block
simple selector
in css2
in selectors-3
single-line flex container
size containment
size containment box
sizing as if empty
sizing function
skyblue
slateblue
slategray
slategrey
small
small kana
snow
soft wrap break
soft wrap opportunity
source
source document
spaces
space-separated matching
space to fill
span count
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
stacking context
stack level
start
starting point
startmost
starts with an ident sequence
starts with a number
starts with a valid escape
start time
start value
start with an ident sequence
start with a number
statement at-rule
'static' media group
static-position containing block
static-position rectangle
stationary scroll
steelblue
step easing function
step position
steps
stop or comma
stretched
strictness value
stroke bounding box
structural pseudo-classes
stuck on the environment
style change event
style rule
style sheet
in css-namespaces-3
in css-speech-1
in css2
stylesheet
subject (of selector)
subjects
subjects of the selector
sub-property
subsequent-sibling combinator
substitute a var()
support
supports queries
switch the fontfaceset to loaded
switch the fontfaceset to loading
synthesize baseline
synthesized baseline
system fonts
table
table caption box
table element
table grid box
tables
table wrapper box
tabs
tab size
tab stop
tabular container
'tactile' media group
tan
target main size
teal
text/css
text node
text sequence
textual data types
thistle
threeddarkshadow
threedface
threedhighlight
threedlightshadow
threedshadow
US