CSS3 is the latest standard for CSS.
CSS3 is completely backwards-compatible with earlier versions of CSS.
CSS3 has been split into “modules”. It contains the “old CSS specification” (which has been split into smaller pieces). In addition, new modules are added.
Some of the most important CSS3 modules are:
Backgrounds and Borders
Image Values and Replaced Content
Multiple Column Layout
Most of the new CSS3 properties are implemented in modern browsers.