CSS (Cascading Style Sheets) is a language which describes how a document written in a markup language looks and how it is formatted. Giving layout, colors and fonts to a document and its elements can change how your website looks and how people think about it. CSS has evolved over time from CSS1 to CSS2 (which is the current standard) to CSS3 (which is still in development). Modern browser support CSS1 and CSS2 but for CSS3 the support is still limited. read more about introduction to css3