Cascading Style Sheets (CSS) is widely used on the Web to define the layout of markup language documents. There are different versions of CSS. For permanent archiving it must be made clear to which files the CSS files refer and which version of CSS is being used. As browser-specific extensions may exist, the target environment of the files must be known, unless only basic elements have been used. If the CSS files contain links to other CSS files or external files, these links must be working.
CSS is a preferred format for file type Markup Language.