The first implementation of CSS was initially drawn up in 1996, was released in 1999, and as of 2001 was supported by all browser releases. The standard for this version, CSS1, was revised again in 2008. Developers began work on the second specification, CSS2, in 1998; its standard was eventually completed in 2007 and then revised again in 2009.
Development of the CSS3 specification commenced in 2001, with features still being proposed as recently as 2009. The development process is likely to continue for some time before a final recommendation for CSS3 is approved. And even though CSS3 isn’t yet complete, people are already beginning to put forward suggestions for CSS4.