CSS1 (Cascade Style Sheet 1) is a norm created in 1996 by the World Wide Web Consortium (W3C).

CSS1 helps to define style sheets which offer a constant and homogeneous HTML page style.

This language is supported by Internet browsers such as Internet Explorer (from 4.0 version) and Netscape (from 4.0x versions).

Note : if a browser doesn't recognize style sheets, it will ignore unknown directives, with a default page settings : no information should be lost.