From http://www.w3schools.com (Copyright Refsnes Data)

W3C CSS Activities

Style sheets define how to display HTML element. CSS is a mechanism for adding style to Web pages.

CSS Tutorial

To learn more about CSS, read our CSS tutorial.

CSS Versions

CSS1

CSS1 became a W3C Recommendation 17. December 1996.

CSS2

CSS2 became a W3C Recommendation 11. January 1999. CSS2 has added support for media (printers and aural devices), downloadable fonts, element-positioning and tables.

CSS3

CSS3 is about breaking CSS into smaller modules.

W3C CSS Specifications and Timeline

Specification	Draft / Proposal	Recommendation

CSS 1		17. Dec 1996
CSS 1 (Revised)		11. Jan 1999

CSS 2		12. May 1998
CSS 2.1	19. Jul 2007
CSS 2 Mobile	08. Dec 2006
CSS 2 TV	14. May 2003
CSS 2 Print	13. Oct 2006

CSS 3	23. May 2001
CSS 3 Namespace	28. Aug 2006
CSS 3 User Interface	11. May 2004
CSS 3 Selectors	15. Des 2005
CSS 3 Fonts	02. Aug 2002
CSS 3 Web Fonts	02. Aug 2002
CSS 3 Colors	14. May 2003
CSS 3 TV	14. May 2003
CSS 3 Backgrounds and borders	16. Feb 2005
CSS 3 Text	06. Mar 2007
CSS 3 Lists	07. Nov 2002
CSS 3 Line	15. May 2002
CSS 3 Box model	09. Aug 2007
CSS 3 Multi column	06. Jun 2007
CSS 3 Ruby	14. May 2003
CSS 3 Border	16. Feb 2005
CSS 3 Speech	16. Dec 2004
CSS 3 Paged Media (PM)	10. Oct 2006
CSS 3 Generated PM	04. May 2007
CSS 3 Print	13. Oct 2006
CSS 3 Values	19. Sep 2006
CSS 3 Cascade	15. Dec 2005
CSS 3 Advanced Layout	09. Aug 2007
CSS 3 Media Queries	06. Jun 2007

W3C Reference:

W3C CSS Home Page