The name CSS comes from the English language for "cascading style sheets", which can be translated as cascading style sheets, styles that can be defined both in the header of a web page and in a separate, individual file. The second option is the recommended one.

CSS is used by both authors and web page readers to define colors, fonts, layouts, and other aspects of document presentation. It is primarily designed to allow the document to be separated as content (written in HTML or a similar Markup Language) from the presentation document (written in CSS).

This separation can improve the accessibility of the content, provide more flexibility and can reduce the maintenance of a website by providing easier control. CSS can also reduce the complexity and repetition of tags used for formatting in the content structure. CSS can also allow the same page to be presented in different playback styles for different media, such as on a computer screen, in print, or in voice (when played back by a screen reader.

With its advent, many web developers have found CSS to be a much more powerful and easy-to-use formatting method, and have found it an outdated tag. In 2006 (Update was done), the capabilities of CSS were considerably improved in terms of the layout design of a web page. However, many websites still use CSS only for text formatting, while they use tables for layout. Because the Internet is growing rapidly, due to the increasing use of mobile phones and PDAs, it is necessary to create web pages accessible to users who use a wide variety of devices. A table-free web design greatly improves accessibility in this regard.

The authority on this type of file is owned by the World Wide Web Consortium (or W3C). They provide complete specifications, a list of browsers that support CSS, validation tools, and information on learning CSS.