CSS 3 is divided into several separate documents called “modules”. Each module adds new capabilities or extends features defined in CSS 2, preserving backward compatibility. As of June 2012, there are over fifty CSS modules published from the CSS Working Group, four of them published as formal recommendations:
2012-06-19 : Media Queries
2011-09-29 : Namespaces
2011-09-29 : Selectors Level 3
2011-06-07 : Color
CSS level 2 revision 1, often referred to as “CSS 2.1”, fixes errors in CSS 2, removes poorly supported or not fully interoperable features and adds already-implemented browser extensions to the specification. After being reviewed by the W3C Advisory Committee, it was finally published as a W3C Recommendation in June 2011.