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What is it?
Cascading Style Sheets (CSS) offers a way of adding styles, such as fonts and colours, to web documents. CSS enables presentation to be separated from content to cope with the different platforms on which web pages are displayed.
According to website accessibility expert Jakob Nielsen, "Web style sheets are cascading, meaning that the site's style sheet is merged with the user's style sheet to create the ultimate presentation.
"These differences make it important that web style sheets are designed by a specialist who understands the many ways the result may look different than what is on his or her own screen."
Style sheets may be external, meaning they can be specified once and applied to all the documents on a website, or embedded within a particular document.
Where did it originate?
CSS began life in 1994 at Cern, the cradle of the web, when H†kon Wium Lie published the first draft of cascading HTML style sheets.
He had the backing of HTML3.0 architect Dave Raggett, who realised that HTML needed a purpose-built page description mechanism. In February 1997 CSS got its own World Wide Web Consortium (W3C) working group. The first commercial browser to support CSS was Microsoft's Internet Explorer 3.
What is it for?
Different style sheets arrive in a series, or cascade, and any single document can end up with style sheets from multiple sources, including the browser, the designer and the user. Cascading order sorts out which set of rules are to influence the presentation.
What makes it special?
CSS gives a greater level of control over how work is presented than with HTML.
How difficult is it to master?
Style sheets can either be hand-written using a text editor or with one of the growing number of web design tools which support CSS. The W3C CSS home page has a list of these tools which include Dreamweaver, Adobe Golive and Homesite. You do not need to know CSS syntax but those who do can fine-tune their style sheets.
Where is it used?
CSS is currently the most widely supported way of styling web documents.
Not to be compared with...
Cascading system failures - the impact of the collapse of one part of an infrastructure on the next.
What systems does it run on?
CSS is supported by most current browsers and web design tools.
Not many people know that...
"CSS is now being taken up, but HTML is in danger again," said Bert Bos, W3C's style sheet activities co-ordinator.
What is coming up?
CSS3, six years in the making, promises to be much simpler to use than CSS2/.2.1.
You should not need to spend much money learning CSS. The World Wide Web Consortium has comprehensive links to tutorials, how-to articles and books by the likes of H†kon Wium Lie, Bert Bos, Dave Raggett and Jakob Nielsen.
Most date back a few years, but remember that the current level, CSS2, has been around since 1997.
Rates of pay
CSS is used by web designers but also sought in software developers, testers and technical authors. Rates vary accordingly.