CSS is a style sheet mechanism that allows authors and readers to attach style (e.g. fonts, colors and spacing) to HTML, XHTML and XML documents. The CSS language is human readable and writable, and expresses style in common desktop publishing terminology.
Finally CSS is an important component in so called "DHTML" and AJAX. Programming Dynamic Web pages may involve dynamic change of CSS features.
See also other articles in the CSS category, for example: