CSS stands for : Cascading Style Sheets. In computing, Cascading Style Sheets (CSS) is a style sheet language used to describe the presentation of a document written in a markup language. It used mostly to style web pages and control how they display. It is compatible with XML documents. Another important use of CSS is positioning elements on a HTML or XHTML page. Instead of having to change a property of an html tag (such as "h1") every single time the tag appears in an HTML page, we can generate a CSS code once, this code will change the properties of every tag. So CSS is also time consuming.