Style sheets contain information on how the content of a webpage (usually stored in XML-based documents) is presented online.

Before the use of style sheets became widespread, the markup of a document would contain information both on the content and the way the content was supposed to be displayed. Through the introduction of style sheets, these two functions were separated, making the markup of the content cleaner and much easier to read and check for consistency. Another benefit of using style sheets is that multiple documents can be connected to the same style sheet, which means that their display would be similar.