What are the current revisions of CSS or what different levels of CSS exist not including unofficial candidate releases?

Answer 1

In terms of official revisions of CSS, you have CSS Level 1 (or CSS1 and became a Recommendation on December 17, 1996) which was the initial CSS version. The next major revision to CSS was the CSS Level 2 Revision 1 (CSS2.1 and became a Recommendation on June 7, 2011). When the World Wide Web Consortium (W3C) began working on the next version of CSS (what is colloquially called CSS3) they decided to break the process into multiple modules allowing different modules to be developed and implemented separately and incrementally. The only modules that have achieved Recommendation status (with the date the module became a Recommendation are in parenthesis) are:

CSS Color Module Level 3 (June 7, 2011)

CSS Namespaces Module Level 3 (September 29, 2011, edited March 20, 2014)

Selectors Level 3 (September 29, 2011)

CSS Print Profile (March 14, 2013)

Media Queries (June 19, 2012)

CSS Style Attributes (November 7, 2013)

There are numerous other modules that are at different steps in the process of becoming Recommendations.