CSS stands for Cascading Style Sheets.Styles define how to display HTML elements.
Styles were added to HTML 4.0 to solve a problem, External Style Sheets can save a lot of work, External Style Sheets are stored in CSS files Styles are normally saved in external .css files. External style sheets enable you to change the appearance and layout of all the pages in a Web site, just by editing one single file!
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:
Selectors
Box Model
Backgrounds and Borders
Image Values and Replaced Content
Text Effects
2D/3D Transformations
Animations
Multiple Column Layout
User Interface
