CSS

===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>.