W3C Recommendation 29 September 2011. CSS (Cascading Style Sheets) is a language for describing the rendering of HTML and XML documents on screen, on paper, in speech, etc. CSS uses Selectors for binding style properties to elements in the document. This document describes the selectors that already exist in CSS1 [CSS1] and CSS2 [CSS21], and further introduces new selectors for CSS3 and other languages that may need them.