CSS

=== Vendor prefixes ===
Individual browser vendors occasionally introduced new parameters ahead of standardization and universalization. To prevent interfering with future implementations, vendors prepended unique names to the parameters, such as <code>-moz-</code> for [[Mozilla Firefox]], <code>-webkit-</code> named after [[WebKit|the browsing engine]] of [[Apple Safari]], <code>-o-</code> for [[Opera Browser]] and <code>-ms-</code> for [[Microsoft Internet Explorer]] and early versions of [[Microsoft Edge]] that use EdgeHTML.

Occasionally, the parameters with vendor prefixes such as <code>-moz-radial-gradient</code> and <code>-webkit-linear-gradient</code> have slightly different syntax as compared to their non-vendor-prefix counterparts.<ref>{{cite web |title=What Are CSS Vendor or Browser Prefixes? |first1= Jennifer |last1=Kyrnin |url=https://www.lifewire.com/css-vendor-prefixes-3466867 |website=Lifewire |language=en |date=2019-11-12 |url-status=live |archive-url=https://web.archive.org/web/20201130084004/https://www.lifewire.com/css-vendor-prefixes-3466867 |archive-date= Nov 30, 2020  }}</ref>

Prefixed properties are rendered obsolete by the time of standardization. Programs are available to automatically add prefixes for older browsers and to point out standardized versions of prefixed parameters. Since prefixes are limited to a small subset of browsers, removing the prefix allows other browsers to see the functionality. An exception is certain obsolete <code>-webkit-</code> prefixed properties, which are so common and persistent on the web that other families of browsers have decided to support them for compatibility.<ref>{{cite web |title=Compatibility Standard |url=https://compat.spec.whatwg.org/ |website=WHATWG |date=24 January 2024 |url-status=live |archive-url=https://web.archive.org/web/20240204073005/https://compat.spec.whatwg.org/ |archive-date= Feb 4, 2024 }}</ref>


[[File:W3C CSS Snapshot.png|thumb|CSS Snapshot 2021]]
CSS has various levels and profiles. Each level of CSS builds upon the last, typically adding new features and typically denoted<ref>{{Cite web |date=7 December 2023 |title=CSS Snapshot 2023 - 2.4. CSS Levels |url=https://www.w3.org/TR/CSS/#css-levels |url-status=live |archive-url=https://web.archive.org/web/20240208172654/https://www.w3.org/TR/CSS/#css-levels |archive-date=Feb 8, 2024 |website=W3C}}</ref>  as CSS&nbsp;1, CSS&nbsp;2, CSS&nbsp;3, and CSS&nbsp;4. Profiles are typically a subset of one or more levels of CSS built for a particular device or user interface. Currently, there are profiles for mobile devices, printers, and television sets. Profiles should not be confused with media types, which were added in CSS&nbsp;2.

====CSS 1====
The first  CSS specification to become an official W3C Recommendation is CSS level 1, published on 17 December 1996.  [[Håkon Wium Lie]] and [[Bert Bos]] are credited as the original developers.<ref>{{cite book|last1=Bos|first2= Håkon |last2=Wium Lie |first1=Bert|title=Cascading style sheets: designing for the Web|date=1997|publisher=Addison Wesley Longman|location=Harlow, England; Reading, MA.|isbn=0-201-41998-X|edition=1st print.|url=https://archive.org/details/cascadingstylesh00lieh}}</ref><ref>[[W3C]]: ''[https://www.w3.org/TR/CSS1 Cascading Style Sheets, level 1] {{Webarchive|url=https://web.archive.org/web/20110209205309/https://www.w3.org/TR/CSS1/ |date=2011-02-09 }} CSS 1 specification''</ref> Among its capabilities are support for

* [[Typeface|Font]] properties such as typeface and emphasis
* Color of text, backgrounds, and other elements
* Text attributes such as spacing between words, letters, and lines of text
* [[alignment (typesetting)|Alignment]] of text, images, [[Table (HTML)|tables]] and other elements
* Margin, border, padding, and positioning for most elements
* Unique identification and generic classification of groups of attributes

The W3C no longer maintains the CSS 1 Recommendation.<ref>[[W3C]]: ''[https://www.w3.org/TR/2008/REC-CSS1-20080411/ Cascading Style Sheets level 1 specification] {{Webarchive|url=https://web.archive.org/web/20110211185814/https://www.w3.org/TR/2008/REC-CSS1-20080411/ |date=2011-02-11 }} CSS level 1 specification''</ref>

====CSS 2====
CSS level 2 specification was developed by the W3C and published as a recommendation in May 1998. A superset of CSS&nbsp;1, CSS&nbsp;2 includes a number of new capabilities like absolute, relative, and fixed positioning of elements and [[z-index]], the concept of media types, support for aural style sheets (which were later replaced by the CSS 3 speech modules)<ref>{{cite web|url=https://www.w3.org/TR/CSS21/aural.html#aural-media-group|title=Aural style sheets|publisher=W3C|access-date=2014-10-26|archive-url=https://web.archive.org/web/20141026010749/https://www.w3.org/TR/CSS21/aural.html#aural-media-group|archive-date=2014-10-26|url-status=live}}</ref> and bidirectional text, and new font properties such as shadows.

The W3C no longer maintains the CSS&nbsp;2 recommendation.<ref>[[W3C]]: ''[https://www.w3.org/TR/2008/REC-CSS2-20080411/ Cascading Style Sheets, level 2] {{Webarchive|url=https://web.archive.org/web/20110116000124/https://www.w3.org/TR/2008/REC-CSS2-20080411/ |date=2011-01-16 }} CSS&nbsp;2 specification (1998 recommendation)''</ref>

====CSS 2.1====
CSS level 2 revision 1, often referred to as "CSS 2.1", fixes errors in CSS&nbsp;2, removes poorly supported or not fully interoperable features and adds already implemented browser extensions to the specification. To comply with the W3C Process for standardizing technical specifications, CSS&nbsp;2.1 went back and forth between Working Draft status and Candidate Recommendation status for many years. CSS 2.1 first became a [https://www.w3.org/TR/2004/CR-CSS21-20040225/ Candidate Recommendation] on 25 February 2004, but it was reverted to a Working Draft on 13 June 2005 for further review. It returned to Candidate Recommendation on 19 July 2007 and then updated twice in 2009. However, because changes and clarifications were made, it again went back to Last Call Working Draft on 7 December 2010.

CSS 2.1 went to Proposed Recommendation on 12 April 2011.<ref>[[W3C]]:''[https://www.w3.org/TR/2011/PR-CSS2-20110412/ Cascading Style Sheets, level 2 revision 1] {{Webarchive|url=https://web.archive.org/web/20111109095352/https://www.w3.org/TR/2011/PR-CSS2-20110412/ |date=2011-11-09 }} CSS 2.1 specification (W3C Proposed Recommendation)''</ref> After being reviewed by the W3C Advisory Committee, it was finally published as a W3C Recommendation on 7 June 2011.<ref name="w3.org">W3C: [https://www.w3.org/2011/05/css-pr.html.en Cascading Style Sheets Standard Boasts Unprecedented Interoperability] {{Webarchive|url=https://web.archive.org/web/20110610221708/https://www.w3.org/2011/05/css-pr.html.en |date=2011-06-10 }}</ref>

CSS 2.1 was planned as the first and final revision of level 2—but low-priority work on CSS 2.2 began in 2015.

====CSS 3====
{{redirect|CSS3}}

Unlike CSS&nbsp;2, which is a large single specification defining various features, CSS&nbsp;3 is divided into several separate documents called "modules". Each module adds new capabilities or extends features defined in CSS&nbsp;2, preserving backward compatibility. Work on CSS level 3 started around the time of publication of the original CSS&nbsp;2 recommendation. The earliest CSS&nbsp;3 drafts were published in June 1999.<ref name="World Wide Web Consortium">{{cite web|url=https://www.w3.org/Style/CSS/specs|title=Descriptions of all CSS specifications|publisher=[[World Wide Web Consortium]]|date=18 February 2011|access-date=3 March 2011|first1=Bert|last1=Bos|author-link1=Bert Bos|archive-url=https://web.archive.org/web/20110331092216/https://www.w3.org/Style/CSS/specs|archive-date=31 March 2011|url-status=live}}</ref>

Due to the modularization, different modules have different stability and statuses.<ref>{{cite web|url=https://www.w3.org/Style/CSS/current-work|title=CSS current work|publisher=[[World Wide Web Consortium]]|date=26 February 2011|access-date=3 March 2011|first1=Bert|last1=Bos|author-link1=Bert Bos|archive-url=https://web.archive.org/web/20110303230112/https://www.w3.org/Style/CSS/current-work|archive-date=3 March 2011|url-status=live}}</ref>

Some modules have ''[[W3C Recommendation#Candidate recommendation (CR)|Candidate Recommendation]]'' (''CR'') status and are considered moderately stable. At ''CR'' stage, implementations are advised to drop vendor prefixes.<ref>{{cite web|url=https://www.w3.org/TR/css-2010/#css|title=Cascading Style Sheets (CSS) Snapshot 2010|publisher=[[World Wide Web Consortium]]|date=12 December 2010|access-date=3 March 2011|first1=Elika J.|last1=Etemad|author-link1=Elika J. Etemad|archive-url=https://web.archive.org/web/20110316103250/https://www.w3.org/TR/css-2010/#css|archive-date=16 March 2011|url-status=live}}</ref>

{| class="wikitable sortable"
|+ Summary of main module-specifications<ref>{{cite web |url=https://www.w3.org/Style/CSS/specs |title=All CSS specifications |publisher=W3C |date=2014-05-22 |access-date=2014-05-30 |archive-url=https://web.archive.org/web/20140530231250/https://www.w3.org/Style/CSS/specs |archive-date=2014-05-30 |url-status=live }}</ref>
|-
!Module
!Specification title
!Status
!Date
|-
|<samp>css3-background</samp>
|[https://www.w3.org/TR/css3-background/ CSS Backgrounds and Borders Module Level 3]&nbsp;
|''Candidate'' Rec. ||align="right"| {{dts|2023|Feb}}
|-
|<samp>css-box-3</samp>
|[https://www.w3.org/TR/css-box-3/ CSS Box Model Module Level 3]
|''Recommendation'' ||align="right"| {{dts|2023|Apr}}

|-
|<samp>css-cascade-3</samp>
|[https://www.w3.org/TR/css-cascade-3/ CSS Cascading and Inheritance Level 3]&nbsp;
|''Recommendation'' ||align="right"| {{dts|2021|Feb}}
|-
|<samp>css-color-3</samp>
|[https://www.w3.org/TR/css3-color CSS Color Module Level 3]
|''Recommendation'' ||align="right"| {{dts|2022|Jan}}
|-
|<samp>css3-content</samp>
|[https://www.w3.org/TR/css-content-3/ CSS Generated Content Module Level 3]&nbsp;
|Working ''Draft'' ||align="right"| {{dts|2019|Aug}}
|-
|<samp>css-fonts-3</samp>
|[https://www.w3.org/TR/css-fonts-3/ CSS Fonts Module Level 3]
|''Recommendation'' ||align="right"| {{dts|2018|Sep}}
|-
|<samp>css3-gcpm</samp>
|[https://www.w3.org/TR/css-gcpm-3/ CSS Generated Content for Paged Media Module]
|Working ''Draft'' ||align="right"| {{dts|2014|May}}
|-
|<samp>css3-layout</samp>
|[https://www.w3.org/TR/css-template-3/ CSS Template Layout Module]
|''Note'' ||align="right"| {{dts|2015|Mar}}
|-
|<samp>css3-mediaqueries</samp>&nbsp;
|[https://www.w3.org/TR/css3-mediaqueries/ Media Queries]
|''Recommendation'' ||align="right"| {{dts|2012|Jun}}
|-
|<samp>mediaqueries-4</samp>&nbsp;
|[https://www.w3.org/TR/mediaqueries-4/ Media Queries Level 4]
|''Candidate'' Rec. ||align="right"| {{dts|2021|Dec}}
|-
|<samp>css3-multicol</samp>&nbsp;
|[https://www.w3.org/TR/css-multicol-1/ Multi-column Layout Module Level 1]
| ''Candidate'' Rec. ||align="right"| {{dts|2021|Oct}}
|-
|<samp>css3-page</samp>
|[https://www.w3.org/TR/css3-page/ CSS Paged Media Module Level 3]
|Working ''Draft'', and part migrated to css3-break ||align="right"| {{dts|2018|Oct}}
|-
|<samp>css3-break</samp>
|[https://www.w3.org/TR/css-break/ CSS Fragmentation Module Level 3]
|''Candidate'' Rec. ||align="right"| {{dts|2018|Dec}}
|-
|<samp>selectors-3</samp>
|[https://www.w3.org/TR/selectors-3/ Selectors Level 3]
|''Recommendation'' ||align="right"| {{dts|2018|Nov}}
|-
|<samp>selectors-4</samp>
|[https://www.w3.org/TR/selectors-4/ Selectors Level 4]
|Working ''Draft'' ||align="right"| {{dts|2022|Nov}}
|-
|<samp>css3-ui</samp>
|[https://www.w3.org/TR/css-ui-3/ CSS Basic User Interface Module Level 3 (CSS3 UI)]
|''Recommendation'' ||align="right"| {{dts|2018|Jun}}
|}

====CSS 4====
{{redirect|CSS4}}

[[File:CSS Standardization - The State of the Web.webm|thumb|[[Jen Simmons]] discussing the state of CSS in 2019, as several CSS{{nbsp}}4 modules were being advanced]]
There is no single, integrated CSS4 specification,<ref>{{cite web|last=Atkins|first=Tab Jr.|title=A Word About CSS4|url=https://www.xanthir.com/b4Ko0|access-date=18 October 2012|archive-url=https://web.archive.org/web/20121031194751/https://www.xanthir.com/b4Ko0|archive-date=31 October 2012|url-status=live}}</ref> because the specification has been split into many separate modules which level independently.

Modules that build on things from CSS Level 2 started at Level 3. Some of them have already reached Level 4 or are already approaching Level 5. Other modules that define entirely new functionality, such as [[Flexbox]],<ref>{{cite web|url=https://www.w3.org/TR/css3-flexbox/|title=CSS Flexible Box Layout Module Level 1|publisher=W3C|date=19 November 2018|access-date=18 October 2012|archive-url=https://web.archive.org/web/20121019153636/https://www.w3.org/TR/css3-flexbox/|archive-date=19 October 2012|url-status=live}}</ref> have been designated as Level 1 and some of them are approaching Level 2.

The CSS Working Group sometimes publishes "Snapshots", a collection of whole modules and parts of other drafts that are considered stable enough to be implemented by browser developers. So far, five such "best current practices" documents have been published as Notes, in 2007,<ref>{{cite web |url=https://www.w3.org/TR/css-beijing/ |title=Cascading Style Sheets (CSS) Snapshot 2007 |date=12 May 2011 |access-date=18 July 2016 |archive-url=https://web.archive.org/web/20160808144255/https://www.w3.org/TR/css-beijing/ |archive-date=8 August 2016 |url-status=live }}</ref> 2010,<ref>{{cite web |url=https://www.w3.org/TR/css-2010/ |title=Cascading Style Sheets (CSS) Snapshot 2010 |date=12 May 2011 |access-date=3 March 2011 |archive-url=https://web.archive.org/web/20110316103250/https://www.w3.org/TR/css-2010/ |archive-date=16 March 2011 |url-status=live }}</ref> 2015,<ref>{{cite web |url=https://www.w3.org/TR/css-2015/ |title=CSS Snapshot 2015 |date=13 October 2015 |website=W3C |access-date=13 February 2017 |archive-url=https://web.archive.org/web/20170127073733/https://www.w3.org/TR/css-2015/ |archive-date=27 January 2017 |url-status=live }}</ref> 2017,<ref>{{cite web |url= https://www.w3.org/TR/css-2017/ |website=W3C  |title= CSS Snapshot 2017 |date= 31 January 2017 |access-date= 13 February 2017 |archive-url= https://web.archive.org/web/20170213164514/https://www.w3.org/TR/css-2017/ |archive-date= 13 February 2017 |url-status= live }}</ref> and 2018.<ref>{{cite web |url=https://www.w3.org/TR/css-2018/ |title=CSS Snapshot 2018 |date=22 January 2019 |website=W3C  |access-date=2 January 2019 |archive-url=https://web.archive.org/web/20190201162518/https://www.w3.org/TR/css-2018/ |archive-date=1 February 2019 |url-status=live }}</ref>

Since these specification snapshots are primarily intended for developers, there has been a growing demand for a similar versioned reference document targeted at authors, which would present the state of interoperable implementations as meanwhile documented by sites like Can I Use...<ref name="caniuse">{{cite web|url=https://caniuse.com/#cats=CSS|website=Can I Use… Support tables for HTML5, CSS3, etc. |title=CSS |access-date=2019-01-26|archive-url=https://web.archive.org/web/20180219074228/https://caniuse.com/#cats=CSS|archive-date=2018-02-19|url-status=live}}</ref> and the MDN Web Docs.<ref name="mdn">{{cite web|url=https://developer.mozilla.org/docs/Web/CSS|website=MDN Web Docs |title=CSS|date=21 July 2023 |url-status=live |archive-url=https://web.archive.org/web/20231126230858/https://developer.mozilla.org/en-US/docs/Web/CSS |archive-date= Nov 26, 2023 }}</ref> A W3C Community Group has been established in early 2020 in order to discuss and define such a resource.<ref name="css4">{{cite web|url=https://www.w3.org/community/css4/|title=Call for Participation in CSS4 Community Group |website=W3C |date=24 February 2020 |access-date=2020-02-27|archive-url=https://web.archive.org/web/20230210062151/https://www.w3.org/community/css4/2020/02/24/call-for-participation-in-css4-community-group/ |archive-date=Feb 10, 2023 |url-status=live}}</ref> The actual kind of [[software versioning|versioning]] is also up to debate, which means that the document, once produced, might not be called "CSS4".