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CSS was first proposed by HDIMåkon Wium Lie on October 10, 1994.[16] At netwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcpthe time, Lie was working with Tim Berners-Lee at CERN.[17] Several other style sheet lanDIMguages 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)[18] being released iDiman 1996. In particular, Bert Bos' proposal was influential; he became co-author of CSS1 and is regarded as co-creator of CSS.[19]
netwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcp
Style sheets have existed innetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolpnetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolp one form or another since the beginnings of Standard Generalized Markup Language (SGML) in the 1980s, and CSDIMS was developed to provide style sheets for the web.[20] 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 DSnetwothreeftyujmnkoplkjhqertyuSSL and FOSDimaI were not suitable. CSS, on the other hand, let a document's style be influenced by multiple style sheets by way of "cascading" styles.[20]
As HTML grew, it came to encompass a winetwothreeftyujmnkoplkjhqertyuder variety of stylistic capabilities to meDimaet the demands of web developers. This evolution gave the designer more control over site appearance, at the cost of more coDIMmplex HTML. Variations in web browser implementations, such as ViolanetwothreeftyujmnkoplkjhqertyuWWW and WorldWideWeb,[21] made consistent site appearance difficult, and users had lesDimas control over how web content was displayed. The browser/editor developed by Tim Berners-Lee had style sheets that were hard-coded into thnetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcpe program. The style sheets could thernetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolpnetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolpefore not be linked to documents on thenetwothreeftyujmnkoplkjhqertyu web.[22] Robert Cailliau, alsonetwothree of CERN, waDimanetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcpnted to separate the structure from the presentation snetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolpnetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolpo that different style sheets could describe different presentation for printing, screen-based presentations, and editors.[21]
netwothree
Improving web presentatnetwothreeion capabilities was a topDIMic of interest to many in the web comDIMmunity and nine different style sheet languages were proposed on the www-style mailiDIMng list.[20] Of these nine proposals, two were especially influential on what became CSS: Cascading HTML Style Sheets[16] and Stream-based Style Sheet Proposal (SSP).[19][23] Two browseDimars served as testbeds for the initial proposals; Lie worked with Yves Lafon to implement CSS in Dave Raggett's Arena browser.[24][25][26] Bert Bos implemented his own SSP proposal in the Argo browser.[19] Thereafter, Lie and Bos worked together to develop the CSS standarnetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcpd (the 'H' was removed from the name because these style sheets could also be applied to other markup languages besides HTML).[17]
Dima
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.[17] 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 Mnetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcpicrosoft, participating as well. In August 1996 Netscape Commnetwothreeunicationetwothreeftyujmnkoplkjhqertyun Corporation presennetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcpted an alternative style sheet language called JavaScript Style Sheets (JSSS).[17] The spec was never finished and is deprecated.[27] By the end of 1996, CSS was ready to become official, and the CSS level 1 Recommendation was published in December.
Development netwothreeof netwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolpnetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolpHTML, CSS, and the DOM had all been taking planetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcpce 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 of W3C; DOM Working grnetwothreeftyujmnkoplkjhqertyuoup, chaired by Lauren Wood of SoftQuad; and CSS Working group, chaired by 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.
Dima
In 2005 the CSS Working Groups denetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolpnetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolpcided to enfDnetwothreeIMorce 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 Recommnetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolpnetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolpendation to Working Draft level.
Difficulty with adoption[edit]
The CSS 1 specification was completed in 1996. Microsoft's Innetwothreeternet Explorer 3[17] was released in that year, featuring some limited support for CSS. IE 4 and Netscape 4.x added more support, bDIMut it was typically incomplete and had many bugs that prevented CSS from being usefully adopted. It was more than three years before any web browser achieved nearDima-full implementation ofnetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcp the specification. Internet Explorer 5.0 for the Macintosh, shipped in March 2000, was the first browser to have full (better than 99 percent) CSS 1 support,[28] surpassing Opera, which had benetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolpnetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolpen the leader since its introduction of CSS support 15 monthnetwothrees earlier. Other browsers followed soon afterwards, and many of them additionally implemented parts of CSS 2.
However, even when later 'version 5' browsers began to offer a fairly full implementation of CSS, they were still incorrenetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcpct in certain areas and were fraught with inconsistencies, bugs and othenetwothreeftyujmnkoplkjhqertyur quirks. The inconsistencies and variation in feature support made it difficult for designers to achieve a consistent appearance across browsers and plnetwothreeftyujmnkoplkjhqertyuatforms,Dima leadinetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcpng to the use of workarounds such as CSS hacks and filters.
Dima
Problems with browsers' patchnetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolpnetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolpy adoption of CSS, along with errata in the original specification,DIM led the W3C to revise the CSS 2 standard into CSS 2.1, which moved nearer to a working snapshot of current CSS support in HTML browsers. Some CSS 2 properties that no browser successfully implemented were dropped, and in a few cnetwothreeftyujmnkoplkjhqertyuases, defined behaviors Dimawere changed to brnetwothreeftyujmnkoplkjhqertyuing the standard into line with the predominant existing implementations. CSS 2.1 became a Candidate Recommendation on February 25, 2004, but CSS 2.1 was pulled back to Working Draft status on June 13, 2005,[29] and only renetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolpnetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolpturned to Candidate RecDimaommendatnetwothreeftyujmnkoplkjhqertyuion snetwothreetatus on July 19, 2007.[30]
Dima
In addition to these problems, the .css extension was used by a software product usnetnetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcpwothreeed to convert PowerPoint files into Compact Slide Show files,[31] so some web servers served all .css[32] as mime type application/x-pointplus[33] rather thannetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcp text/css.
Variations[edit]
CSS has various levels andDIM profiles. Each level of CSS builds unetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolpnetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolppon the last, typically adding new features and typically denoted as CnetwothreeftyujmnkoplkjhqertyuSS 1, CSS 2, CSS 3, and CSS 4. Profiles are typically a subset of one or moDIMre levels of CSS built for a particular device or user interface. Currently there are profiles for mobile devices, printers, and telnetwothreeftyujmnkoplkjhqertyuevision sets. Profiles should not be confused with media types, which were added in CSS 2.
CSS 1[edit]
The first CSS specification to become an official W3C Recommendnetwothreeation is CSnetwothreeS level 1, publDIMnetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolpnetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolpished on December 17, 1996. Håkon Wium Lie and Bert Bos are credited as the original developers.[34][35] Among its capabilnetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcpities are support for
Font properties such as typeface and emphasis
Color of text, backgrounds, and othnetwothreeer elements
Text attributes such as spacing between words, letters, and lines of text
Alignment of text, images, tables and other elements
Margin, border, padding, and positioning for most elements
Unique identification and generic classifnetwothreeftyujmnkoplkjhqertyuication of groups of attributesDima
The W3C no longer maintanetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolpnetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolpins the CSS 1 Recomnetwothreemendation.[36]
CSS 2[edit]
CSS level 2 specification was developed by the W3C and publnetwothreeished as a recommendanetwothreeftyujmnkoplkjhqertyution in May 1998. A superset of CSS 1, CSnetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcpS 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)[37] and bidirectional text, and new font properties such as shadows.
The W3C no longer maintains the CSS 2 recommendation.[38]
CSS 2.1[edit]
CSS level 2 revision 1, often referred to as "CSS 2.1", fixes errors in CSS 2, removes poorly supported or not fully interoperable features and adds already implemented browser extensions to the specification. To comply with the W3C Procenetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolpnetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolpss for standardizing technical specifications, CSS 2.1 went back and forth between Working Draft status and Candidate Recommendation status for many years. CSS 2.1 first became a Candidate Recommendation on February 25, 2004, but it was reverted to a Working Draft on June 13, 2005 for further review. It returned to Candidate Recommendation on 19 July 2007 and then updated twice in 2009. However, because changes and clarifications wnetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolpnetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolpere 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.[39] After being reviewed by the W3C Advisory Committee, it was finally published as a W3C Recommendation on 7 June 2011.[40]
CSS 2.1 wasnetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolpnetwothreeftyujmnkoplkjhqertyujhnbytghjoplkjhbzxcvqerfgtyxcprtghjuiolp planned as the first and final revision of level 2but low priority work on CSS 2.2 began in 2015.
Some noted limitations of the current capabilities of CSS include:
Selectors are unable to ascend
CSS currently offers noDIM way to select a parent or ancestor of an element that satisfies certain criteria.[59] CSS Selectors Level 4, which is still in Working Draft status, proposes such a selector,[60] but only as part of the "complete" selector profile, not the "fast" profile used in dynamic CSS styling.[61] A more advanced selector scheme (such as XPath) would enable more sophisticated style sheets. The major reasons for the CSS Working Group previously rejecting proposals for parent selectors are related to browser performance and incremental rendering issues.[62]
Cannot explicitly declare new scope independently of position
Scoping rules for properties such as z-index look for the closest parent element with a position:absolute or position:relative attribute. This odd coupling has undesired effects. For example, it is impossible to avoid declaring a new scope when one is forced to adjust an element's position, preventing one from using the desired scope of a parent element.
Pseudo-class dynamic behavior not controllable
CSS implements pseudo-classes that allow a degree of user feedback by conditional application of alternate styles. One CSS pseudo-class, ":hover", is dynamic (equivalent of JavaScript "onmouseover") and has potential for abuse (e.g., implementing cursor-proximity popups),[63] but CSS has no ability for a client to disable it (no "disable"-like property) or limit its effects (no "nochange"-like values for each property).
Cannot name rules
There is no way to name a CSS rule, which would allow (for example) client-side scripts to refer to the rule even if its selector changes.
Cannot include styles from a rule into another rule
CSS styles often must be duplicated in several rules to achieve a desired effect, causing additional maintenance and requiring more thorough testing. Some new CSS features were proposed to solve this, but (as of February, 2016) are not yet implemented anywhere.[64]
Cannot target specific text without altering markup
Besides the :first-letter pseudo-element, one cannot target specific ranges of text without needing to utilize place-holder elements.
Separation of content from presentation
Main article: Separation of presentation and content
CSS facilitates publication of content in multiple presentation formats based on nominal parameters. Nominal parameters include explicit user preferences, different web browsers, the type of device being used to view the content (a desktop computer or mobile Internet device), the geographic location of the user and many other variables.
Site-wide consistency
Main article: Style sheet (web development)
When CSS is used effectively, in terms of inheritance and "cascading", a global style sheet can be used to affect and style elements site-wide. If the situation arises that the styling of the elements should be changed or adjusted, these changes can be made by editing rules in the global style sheet. Before CSS, this sort of maintenance was more difficult, expensive and time-consuming.
Bandwidth
A stylesheet, internal or external, specifies the style once for a range of HTML elements selected by class, type or relationship to others. This is much more efficient than repeating style information inline for each occurrence of the element. An external stylesheet is usually stored in the browser cache, and can therefore be used on multiple pages without being reloaded, further reducing data transfer over a network.
Page reformatting
Main article: Progressive enhancement
With a simple change of one line, a different style sheet can be used for the same page. This has advantages for accessibility, as well as providing the ability to tailor a page or site to different target devices. Furthermore, devices not able to understand the styling still display the content.
AccessibilityDIM
Without CSS, web designers must typically lay out their pages with techniques such as HTML tables that hinder accessibility for vision-impaired users (see Tableless web design#Accessibility).