CSS3 Introduction
is fully backwards compatible with CSS3, so you don’t have to change your existing design. Browsers will always support CSS2.
CSS3 Modules
CSS3 is split into "modules". Old specifications have been broken into small pieces and new ones have been added.
Some of the most important CSS3 modules are as follows:
Selector
Box model
Background and border
Text effects
2D/3D conversion
Animation
Multi-column layout
User interface
CSS3 Recommendation
The W3C CSS3 specification is still there development.
However, many new CSS3 properties are available in modern browsers.