Cascading Style Sheets
CSS is a style sheet language used to describe the presentation of a document written in a markup language. The most common application of CSS is in styling Web pages written in HTML and Extensible Hypertext Markup Language (XHTML), but the language can be applied to any kind of Extensible Markup Language (XML) document, including Scalable Vector Graphics (two-dimensional graphics) and XML User Interface Language (XUL), which was developed by Mozilla.
CSS is a simple mechanism to add style (fonts, colors, and spacing) to Web documents. Style sheets describe how documents are presented on screens, in print, or how they are pronounced. W3C has actively promoted the use of style sheets on the Web since the Consortium was founded in 1994.