Cascading Style Sheets (CSS) is a standard (or language) that describes the formatting of markup language pages. CSS defines formatting for the following document types:
- HyperText Markup Language (HTML)
- Extensible HyperText Markup Language (XHTML)
- Extensible Markup Language (XML)
- Scalable Vector Graphic (SVG)
- XML User Interface Language (XUL)
CSS enables developers to separate content and visual elements for greater page control and flexibility. A CSS file is normally attached to an HTML file by means of a link in the HTML file.
In December 1998, the World Wide Web Consortium (W3C) published the first CSS specification (CSS1). This was followed by CSS Level 2 (CSS2), and CSS Level 2, Revision 1 (CSS2.1)
HTML document formatting was tedious and complex before CSS because of built-in HTML style attributes. Specifically, styled tags required detailed and repetitious descriptions of the following elements:
- Font colors
- Background styles
- Element alignments
- Borders
- Sizes
CSS structurally defines elements for headings (h1), sub-headings (h2), sub-sub-headings (h3), etc. Element options are available for font, color, emphasis, size, etc.
CSS allows developers to move styling elements to a separate HTML area for clean markup. For example, if a developer wanted to change the font for all h2 headings in an HTML file, a single change could be made to the attached CSS file. If no CSS file was attached, the developer would have to change the font option for each h2 heading in the main HTML file.
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