CSS Basics - The CSS - page 11

The process to make it to a Recommendation can be quite drawn out.
Although CSS3 is big on everyone's mind, CSS 2.1 is just now ready to
become a Proposed Recommendation, so it is sometimes hard to nail
down by specification alone what is ready for you to spend time to learn
or to use on a site.
Here is where the various specifications are along that line and that you
can start using today:
■ CSS2 : CSS2 became a Recommendation in 1998. As a specification, it
has been superseded by CSS2.1, though the term “CSS2” may be used
to refer to either.
■ CSS2.1 : As this topic is being written in the later part of 2010, the CSS2.1
specification is being readied for PR status. CSS2.1 made changes to
CSS2 by updating technical descriptions and removing properties to
better reflect implementation (or total lack of implementation) of the
previous Recommendation.
■ CSS3 : With CSS3, the specification has been split into modules as a way
to control the complexity of any given piece of the large undertak-
ing as well as provide user agents a clear means to carve out which
areas they may not support due to technical device limitations. Some
modules are CRs with better support and implementations, and others
have yet to be written.
For the updated status of CSS2.1 and the various CSS3 modules, see
http://www.w3.org/Style/CSS/current-work . And with all these specifica-
tions, CSS3 modules in particular, refer not just to the specification status
but also to browser compatibility charts for implementation details on
the various properties you may want to use.