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== History ==

Style sheets have existed in one form or another since the beginnings of [[SGML]] in the 1970s. Cascading Style Sheets were developed as a means for creating a consistent approach to providing style information for web documents.

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 but at the cost of HTML becoming more complex to write and maintain. Variations in [[web browser]] implementations made consistent site appearance difficult, and users had less control over how web content was displayed.

To improve the capabilities of web presentation, nine different style sheet languages were proposed to the W3C's www-style mailing list. Of the nine proposals, two were chosen as the foundation for what became CSS: ''Cascading HTML Style Sheets'' (CHSS) and ''Stream-based Style Sheet Proposal'' (SSP). First, [[HÃ¥kon Wium Lie]] (now the [[Chief Technical Officer|CTO]] of [[Opera Software]]) proposed Cascading HTML Style Sheets (CHSS) in October 1994, a language which has some resemblance to today's CSS. [[Bert Bos]] was working on a browser called [[Argo (web browser)|Argo]] which used its own style sheet language, Stream-based Style Sheet Proposal (SSP). Lie and Bos worked together to develop the CSS standard (the 'H' was removed from the name because these style sheets could be applied to other markup languages besides HTML).

Unlike existing style languages like [[Document Style Semantics and Specification Language|DSSSL]] and [[FOSI]], CSS allowed a document's style to be influenced by multiple style sheets. One style sheet could [[inheritance (computer science)|inherit]] or "cascade" from another, permitting a mixture of stylistic preferences controlled equally by the site designer and user.

HÃ¥kon's proposal was presented at the "Mosaic and the Web" conference in [[Chicago, Illinois]] in 1994, and again with Bert Bos in 1995. Around this time, the [[World Wide Web Consortium]] was being established; the W3C took an interest in the development of CSS, and 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). HÃ¥kon and Bert were the primary technical staff on this aspect of the project, with additional members, including Thomas Reardon of [[Microsoft]], participating as well. 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 group]]s: HTML Working group, chaired by [[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 2008]].

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

=== Difficulty with adoption ===

Although the CSS1 specification was completed in 1996 and Microsoft's [[Internet Explorer 3]] was released in that year featuring some limited support for CSS, it would be more than three years before any web browser achieved near-full implementation of the specification. [[Internet Explorer 5|Internet Explorer 5.0]] for the [[Apple Macintosh|Macintosh]], shipped in March 2000, was the first browser to have full (better than 99 percent) CSS1 support{{Fact|date=June 2008}}, surpassing [[Opera (web browser)|Opera]], which had been the leader since its introduction of CSS support 15 months earlier. Other browsers followed soon afterwards, and many of them additionally implemented parts of CSS2. As of July 2008, no (finished) browser has fully implemented CSS2, with implementation levels varying (see [[Comparison of layout engines (CSS)]]). 

Even though early browsers such as [[Internet Explorer 3]] and [[Internet Explorer 4|4]], and [[Netscape Navigator|Netscape 4.x]] had support for CSS, it was typically incomplete and afflicted with serious [[Software bug|bugs]]. This was a serious obstacle for the adoption of CSS.

When later 'version 5' browsers began to offer a fairly full implementation of CSS, they were still incorrect in certain areas and were fraught with inconsistencies, bugs and other quirks. The proliferation of such CSS-related inconsistencies and even the variation in feature support has made it difficult for designers to achieve a consistent appearance across platforms. Some authors commonly resort to using some [[workaround]]s such as CSS hacks and [[CSS filter]]s in order to obtain consistent results across web browsers and [[System platform|platforms]].

Problems with browsers' patchy adoption of CSS along with errata in the original specification led the W3C to revise the CSS2 standard into CSS2.1, which may be regarded as something nearer to a working snapshot of current CSS support in HTML browsers. Some CSS2 properties which no browser had successfully implemented were dropped, and in a few cases, defined behaviours were changed to bring the standard into line with the predominant existing implementations. CSS2.1 became a Candidate Recommendation on [[February 25]], [[2004]], but css-21 was pulled back to Working Draft status on [[June 13]], [[2005]],<ref>[http://annevankesteren.nl/2005/06/ Archives June 2005 - Anneâ€™s Weblog<!-- Bot generated title -->]</ref> and only returned to Candidate Recommendation status on [[July 19]], [[2007]].<ref>[http://www.w3.org/News/2007#item Archive of W3C News in 2007<!-- Bot generated title -->]</ref>

In the past, some web servers were configured to serve all documents with the filename extension <code>.css</code> as mime type <code>application/x-pointplus</code> rather than <code>text/css</code>. At the time, the Net-Scene company was selling PointPlus Maker to convert [[Microsoft PowerPoint|PowerPoint]] files into Compact Slide Show files (using a <code>.css</code> extension).{{Fact|date=July 2008}}

=== Variations ===

CSS has various levels and profiles. Each level of CSS builds upon the last, typically adding new features and typically denoted as CSS1, CSS2, and CSS3. 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 CSS2.

==== CSS 1 ====

The first CSS specification to become an official W3C Recommendation is CSS level 1, published in December 1996.<ref>[[W3C]]: ''[http://www.w3.org/TR/CSS1 Cascading Style Sheets, level 1] 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 maintains the CSS1 Recommendation.<ref>[[W3C]]: ''[http://www.w3.org/Style/CSS/ Cascading Style Sheets, home page] CSS Home Page''</ref>

==== CSS 2 ====

CSS level 2 was developed by the W3C and published as a Recommendation in May 1998. A superset of CSS1, CSS2 includes a number of new capabilities like absolute, relative, and fixed [[positioning]] of elements, the concept of media types, support for aural style sheets and bidirectional text, and new font properties such as shadows. The W3C maintains the CSS2 Recommendation.<ref>[[W3C]]: ''[http://www.w3.org/TR/REC-CSS2/ Cascading Style Sheets, level 2] CSS 2 specification''</ref>

CSS level 2 revision 1 or CSS 2.1 fixes errors in CSS2, removes poorly-supported features and adds already-implemented browser extensions to the specification. While it was a [http://www.w3.org/TR/CSS21/ Candidate Recommendation] for several months, on [[June 15]], [[2005]] it was reverted to a working draft for further review.<ref>[[W3C]]: ''[http://www.w3.org/TR/CSS21 Cascading Style Sheets, level 2 revision 1] CSS 2.1 specification''</ref>  It was returned to Candidate Recommendation status on [[19 July]] [[2007]].

==== CSS 3 ====

CSS level 3 is currently under [[Software development process|development]].<ref>[[W3C]]: ''[http://www.w3.org/Style/CSS/current-work CSS: under construction]'', CSS 3, etc.</ref> The W3C maintains a [http://www.w3.org/Style/CSS/current-work#table CSS3 progress report]. CSS3 is modularized and will consist of several separate Recommendations. The W3C CSS3 Roadmap provides a summary and introduction.<ref>[http://www.w3.org/TR/css3-roadmap/ Introduction to CSS3, W3C Working Draft, 23 May 2001]</ref>

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