CSS

==History==
[[File:Håkon Wium Lie.jpg|thumb|right|upright|[[Håkon Wium Lie]], chief technical officer of the Opera Software company and co-creator of the CSS web standards]]

CSS was first proposed by [[Håkon Wium Lie]] on 10 October 1994.<ref name="chss-proposal">{{cite web|last=Lie|first=Hakon W|title=Cascading HTML style sheets – a proposal|date=10 October 1994|issue=92|url=https://www.w3.org/People/howcome/p/cascade.html|access-date=25 May 2014|publisher=CERN|format=Proposal|archive-url=https://web.archive.org/web/20140604022945/https://www.w3.org/People/howcome/p/cascade.html|archive-date=4 June 2014|url-status=live}}</ref> At the time, Lie was working with [[Tim Berners-Lee]] at [[CERN]].<ref name="chapter20">{{cite book|title=Cascading Style Sheets, designing for the Web|year=1999|publisher=Addison Wesley|isbn=0-201-59625-3|url=https://archive.org/details/cascadingstyles000lieh|access-date=23 June 2010|author-link1=Håkon Wium Lie|first1=Håkon Wium|last1=Lie|author-link2=Bert Bos|first2=Bert|last2=Bos}}</ref> Several other style sheet languages for the web were proposed around the same time, and discussions on public mailing lists and inside [[World Wide Web Consortium]] resulted in the first W3C CSS Recommendation (CSS1)<ref name="w3c-css1">{{cite web|title=Cascading Style Sheets, level 1|url=https://www.w3.org/TR/1999/REC-CSS1-19990111|publisher=World Wide Web Consortium|access-date=2014-03-07|archive-url=https://web.archive.org/web/20140409234430/https://www.w3.org/TR/1999/REC-CSS1-19990111|archive-date=2014-04-09|url-status=live}}</ref> being released in 1996. In particular, a proposal by [[Bert Bos]] was influential; he became co-author of CSS1, and is regarded as co-creator of CSS.<ref name="WWW3">{{cite web|title=Simple style sheets for SGML & HTML on the web|url=https://www.w3.org/People/Bos/style.html|publisher=World Wide Web Consortium|access-date=20 June 2010|author-link=Bert Bos|first=Bert|last=Bos|date=14 April 1995|archive-url=https://web.archive.org/web/20090923221609/https://www.w3.org/People/Bos/style.html|archive-date=23 September 2009|url-status=live}}</ref>

Style sheets have existed in one form or another since the beginnings of Standard Generalized Markup Language ([[SGML]]) in the 1980s, and CSS was developed to provide style sheets for the web.<ref name="css-phd">{{cite web|title=Cascading Style Sheets|url=https://people.opera.com/howcome/2006/phd/|publisher=University of Oslo|access-date=3 September 2014|archive-url=https://web.archive.org/web/20060906211843/https://people.opera.com/howcome/2006/phd/|archive-date=2006-09-06|url-status=dead}}</ref> One requirement for a web style sheet language was for style sheets to come from different sources on the web. Therefore, existing style sheet languages like [[Document Style Semantics and Specification Language|DSSSL]] and [[Formatting Output Specification Instance|FOSI]] were not suitable. CSS, on the other hand, let a document's style be influenced by multiple style sheets by way of "cascading" styles.<ref name="css-phd"/>

As HTML grew, it came to encompass a wider variety of stylistic capabilities to meet the demands of [[web development|web developers]]. This evolution gave the designer more control over site appearance, at the cost of more complex HTML. Variations in [[web browser]] implementations, such as [[ViolaWWW]] and [[WorldWideWeb]],<ref name="IEEE">{{cite web|last1=Petrie|first1=Charles|title=Interview Robert Cailliau on the WWW Proposal: "How It Really Happened."|url=https://www.computer.org/portal/web/computingnow/ic-cailliau |publisher=[[Institute of Electrical and Electronics Engineers]]|access-date=18 August 2010|author-link2=Robert Cailliau|first2=Robert|last2=Cailliau|date=November 1997|archive-url=https://web.archive.org/web/20110106041256/https://www.computer.org/portal/web/computingnow/ic-cailliau |archive-date=6 January 2011|url-status=dead}}</ref> made consistent site appearance difficult, and users had less control over how web content was displayed. The browser/editor developed by Tim Berners-Lee had style sheets that were hard-coded into the program. The style sheets could therefore not be linked to documents on the web.<ref name= "chapter20" /> [[Robert Cailliau]], also of CERN, wanted to separate the structure from the presentation so that different style sheets could describe different presentation for printing, screen-based presentations, and editors.<ref name="IEEE" />

Improving web presentation capabilities was a topic of interest to many in the web community and nine different style sheet languages were proposed on the www-style mailing list.<ref name="css-phd"/> Of these nine proposals, two were especially influential on what became CSS: Cascading HTML Style Sheets<ref name="chss-proposal" /> and Stream-based Style Sheet Proposal (SSP).<ref name="WWW3"/><ref name=ssp>{{cite web|title=Stream-based Style sheet Proposal|url=https://www.w3.org/People/Bos/stylesheets.html|access-date=3 September 2014|author-link=Bert Bos|first=Bert|last=Bos|date=31 March 1995|archive-url=https://web.archive.org/web/20141012131653/https://www.w3.org/People/Bos/stylesheets.html|archive-date=12 October 2014|url-status=live}}</ref> Two browsers served as testbeds for the initial proposals; Lie worked with [[Yves Lafon]] to implement CSS in [[Dave Raggett]]'s [[Arena (web browser)|Arena]] browser.<ref>{{cite web|title=Libwww Hackers|url=https://www.w3.org/Library/Collaborators.html|publisher=World Wide Web Consortium|access-date=6 June 2010|author-link=Henrik Frystyk Nielsen|first=Henrik Frystyk|last=Nielsen|date=7 June 2002|archive-url=https://web.archive.org/web/20091202042207/https://www.w3.org/Library/Collaborators.html|archive-date=2 December 2009|url-status=live}}</ref><ref>{{cite web|url=https://www.w3.org/People/Lafon/|title=Yves Lafon|access-date=17 June 2010|publisher=World Wide Web Consortium|archive-url=https://web.archive.org/web/20100624003146/https://www.w3.org/People/Lafon/|archive-date=24 June 2010|url-status=live}}</ref><ref>{{cite web|url=https://www.w3.org/People/domain?domain=Technology+and+Society|title=The W3C Team: Technology and Society|publisher=World Wide Web Consortium|access-date=22 January 2011|date=18 July 2008|archive-url=https://web.archive.org/web/20100528051449/https://www.w3.org/People/domain?domain=Technology+and+Society|archive-date=28 May 2010|url-status=live}}</ref> Bert Bos implemented his own SSP proposal in the [[Argo (web browser)|Argo]] browser.<ref name="WWW3"/> Thereafter, Lie and Bos worked together to develop the CSS standard (the 'H' was removed from the name because these style sheets could also be applied to other markup languages besides HTML).<ref name="chapter20"/>

Lie's proposal was presented at the "[[Mosaic and the Web]]" conference (later called WWW2) in Chicago, Illinois in 1994, and again with Bert Bos in 1995.<ref name="chapter20" /> Around this time the W3C was already being established and took an interest in the development of CSS. It organized a workshop toward that end chaired by [[Steven Pemberton]]. This resulted in W3C adding work on CSS to the deliverables of the HTML editorial review board (ERB). Lie and Bos were the primary technical staff on this aspect of the project, with additional members, including [[Thomas Reardon]] of Microsoft, participating as well. In August 1996, [[Netscape|Netscape Communication Corporation]] presented an alternative style sheet language called [[JavaScript Style Sheets]] (JSSS).<ref name="chapter20" /> The spec was never finished, and is deprecated.<ref>{{cite web|title=JavaScript-Based Style Sheets|url=https://www.w3.org/Submission/1996/1/WD-jsss-960822|publisher=W3C|access-date=23 June 2010|author=[[Lou Montulli]]|author2=[[Brendan Eich]]|author3=[[Scott Furman]]|author4=[[Donna Converse]]|author5=[[Troy Chevalier]]|date=22 August 1996|archive-url=https://web.archive.org/web/20100527213412/https://www.w3.org/Submission/1996/1/WD-jsss-960822|archive-date=27 May 2010|url-status=live}}</ref> By the end of 1996, CSS was ready to become official, and the CSS level 1 Recommendation was published in December.

Development of HTML, CSS, and the [[Document Object Model|DOM]] had all been taking place in one group, the HTML Editorial Review Board (ERB). Early in 1997, the ERB was split into three working groups: [[HTML Working Group]], chaired by [[Dan Connolly (computer scientist)|Dan Connolly]] of W3C; DOM Working group, chaired by Lauren Wood of [[SoftQuad]]; and [[CSS Working Group]], chaired by [[Chris Lilley (W3C)|Chris Lilley]] of W3C.

The CSS Working Group began tackling issues that had not been addressed with CSS level 1, resulting in the creation of CSS level 2 on November 4, 1997. It was published as a W3C Recommendation on May 12, 1998. CSS level 3, which was started in 1998, is still under development {{as of|2014|lc=y}}.

In 2005, the CSS Working Groups decided to enforce the requirements for standards more strictly. This meant that already published standards like CSS&nbsp;2.1, CSS&nbsp;3 Selectors, and CSS&nbsp;3 Text were pulled back from Candidate Recommendation to Working Draft level.

===Difficulty with adoption===
The CSS&nbsp;1 specification was completed in 1996. Microsoft's [[Internet Explorer 3]]<ref name="chapter20" /> was released that year, featuring some limited support for CSS.  [[Internet Explorer 4|IE 4]] and [[Netscape Navigator|Netscape 4.x]] added more support, but it was typically incomplete and had many [[Software bug|bugs]] that prevented CSS from being usefully adopted. It was more than three years before any web browser achieved near-full implementation of the specification. [[Internet Explorer for Mac|Internet Explorer 5.0]] for the [[Apple Macintosh|Macintosh]], shipped in March 2000, was the first browser to have full (better than 99 percent) CSS&nbsp;1 support,<ref>{{cite web|title=CSS software|publisher=W3C|url=https://www.w3.org/Style/CSS/software.en.html#w26|access-date=2011-01-15|archive-url=https://web.archive.org/web/20101125162013/https://www.w3.org/Style/CSS/software.en.html#w26|archive-date=2010-11-25|url-status=live}}</ref> surpassing [[Opera (web browser)|Opera]], which had been the leader since its introduction of CSS support fifteen months earlier. Other browsers followed soon afterward, and many of them additionally implemented parts of CSS&nbsp;2.

However, even when later "version 5" web browsers began to offer a fairly full implementation of CSS, they were still incorrect in certain areas. They were fraught with inconsistencies, bugs, and other [[Quirks mode|quirks]]. [[Internet Explorer 5|Microsoft Internet Explorer 5. x for Windows]], as opposed to the very different [[Internet Explorer for Mac|IE for Macintosh]], had a flawed implementation of the [[CSS box model]], as compared with the CSS standards. Such inconsistencies and variation in feature support made it difficult for designers to achieve a consistent appearance across browsers and [[Computing platform|platform]]s without the use of [[workaround]]s termed [[CSS hack|CSS hacks and filters]]. The IE Windows box model bugs were so serious that, when [[Internet Explorer 6]] was released, Microsoft introduced a backward-compatible mode of CSS interpretation ("[[quirks mode]]") alongside an alternative, corrected "standards mode". Other non-Microsoft browsers also provided mode-switch capabilities. It, therefore, became necessary for authors of [[HTML]] files to ensure they contained special distinctive [[Document type declaration#HTML5 DTD-less DOCTYPE|"standards-compliant CSS intended" marker]] to show that the authors intended CSS to be interpreted correctly, in compliance with standards, as opposed to being intended for the now long-obsolete [[Internet Explorer 5|IE5/Windows browser]]. Without this marker, web browsers with the "quirks mode"-switching capability will size objects in web pages as IE 5 on Windows would, rather than following CSS standards.

Problems with the patchy adoption of CSS and errata in the original specification led the W3C to revise the CSS&nbsp;2 standards into CSS&nbsp;2.1, which moved nearer to a working snapshot of current CSS support in HTML browsers. Some CSS&nbsp;2 properties that no browser successfully implemented were dropped, and in a few cases, defined behaviors were changed to bring the standard into line with the predominant existing implementations. CSS&nbsp;2.1 became a Candidate Recommendation on February 25, 2004, but CSS&nbsp;2.1 was pulled back to Working Draft status on June 13, 2005,<ref>{{cite web|url=https://annevankesteren.nl/2005/06/css-21|title=CSS 2.1&nbsp;– Anne's Weblog|author=[[Anne van Kesteren]]|access-date=2011-02-16|archive-url=https://web.archive.org/web/20051210101312/https://annevankesteren.nl/2005/06/css-21|archive-date=2005-12-10|url-status=live}}</ref> and only returned to Candidate Recommendation status on July 19, 2007.<ref>{{cite web|access-date=2011-02-16|archive-date=2011-06-28|archive-url=https://web.archive.org/web/20110628191558/https://www.w3.org/News/2007.html#entry-7058|publisher=[[World Wide Web Consortium]]|title=Archive of W3C News in 2007|url=https://www.w3.org/News/2007.html#entry-7058|url-status=live}}</ref>

In addition to these problems, the <code>.css</code> extension was used by a software product used to convert [[Microsoft PowerPoint|PowerPoint]] files into Compact Slide Show files,<ref>{{cite web|last=Nitot |first=Tristan |title=Incorrect MIME Type for CSS Files |url=https://developer.mozilla.org/en/Incorrect_MIME_Type_for_CSS_Files |work=[[Mozilla Developer Center]] |publisher=[[Mozilla]] |access-date=20 June 2010 |date=18 March 2002 |archive-url=https://web.archive.org/web/20110520044919/https://developer.mozilla.org/en/Incorrect_MIME_Type_for_CSS_Files |archive-date=2011-05-20 |url-status=dead }}</ref>
so some web servers served all <code>.css</code><ref>{{cite web|last=McBride|first=Don|title=File Types|url=https://donsnotes.com/tech/filetype.html|access-date=20 June 2010|date=27 November 2009|archive-url=https://web.archive.org/web/20101029155135/https://donsnotes.com/tech/filetype.html|archive-date=29 October 2010|url-status=live}}</ref> as [[Internet media type|MIME type]] <code>application/x-pointplus</code><ref>{{cite web|title=css file extension details|url=https://extensions.pndesign.cz/css-file|publisher=File extension database|access-date=20 June 2010|date=12 March 2010|archive-url=https://web.archive.org/web/20110718182554/https://extensions.pndesign.cz/css-file|archive-date=18 July 2011|url-status=dead}}</ref> rather than <code>text/css</code>.

=== 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".