About CSS (Style Cascading Sheets)

CSS

     Cascading Style Sheets (CSS) is a style sheet language used to describe the look and formatting of a document written in a markup language. Its most common application is to style web pages written in HTML and XHTML.

     CSS is designed primarily to enable the separation of document content (written in HTML or a similar markup language) from document presentation, including elements such as the layout, colors, and fonts. This separation can improve content accessibility, provide more flexibility and control in the specification of presentation characteristics, enable multiple pages to share formatting, and reduce complexity and repetition in the structural content (such as by allowing for tableless web design). 

    CSS can also allow the same markup page to be presented in different styles for different rendering methods, such as on-screen, in print, by voice (when read out by a speech-based browser or screen reader) and on Braille-based, tactile devices. While the author of a document typically links that document to a CSS style sheet, readers can use a different style sheet, perhaps one on their own computer, to override the one the author has specified.

     CSS specifies a priority scheme to determine which style rules apply if more than one rule matches against a particular element. In this so-called cascade, priorities or weights are calculated and assigned to rules, so that the results are predictable.

Levels (versions)


     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 level 1 (1996, 1999) contains properties for fonts, margins, colors, etc., that nearly all profiles of CSS need.

     CSS level 2 revision 1 (“CSS 2.1”) contains all of CSS level 1 and adds absolutely positioned elements, automatic numbering, page breaks, right to left text and other things. At this moment, September 2009, it is a Candidate W3C Recommendation.

     CSS level 3 is under development. It includes all of level 2 and extends it with new selectors, fancy borders and backgrounds, vertical text, user interaction, speech and much more.

Need more? Read CSS common mistakes for beginners