Cascading Style Sheets (CSS) are used to increase the efficiency of web pages and to make the structure and alterations easier. The rendering of the web pages are brought together into, typically, one file. Here the definitions for the colours and styles to be used on the web pages are defined.

By bringing this information together in this way we only have to write it the once. Also, because it is held in a separate file browsers will cache the information, reducing the load on our server.