There are a number of very good CSS-related resources available on the Web. Here are some of them.
These resources provide a good overview of what’s happening in the world of CSS or otherwise provide you with a broad look at CSS.
When all else fails, you can always use the source, Luke. The specifications contain, albeit in a somewhat terse and not always easily decipherable form, the complete description of how conforming user agents should handle CSS. They also contain a complete CSS parsing grammar and forward-compatible parsing rules, both of which are invaluable to the people who write user agents but of minimal interest to almost everyone else.
This is, officially speaking, the online center of the CSS universe. There are links to the CSS Recommendations, to new ideas under consideration, and to other sites about CSS. There are links to historical style sheet proposals, to information about current usage and implementations of CSS, and more. There are also lists of books about CSS, news of new CSS tools, and many other useful bits of information.
This presents a fairly complete set of pages designed to test any CSS implementation. Each page of the suite tests various aspects of CSS properties, one property per page. The tests were largely developed ...