What is CSS3
"A web page consists of markup TML (HyperText Markup Language) that describes the meaning of the content on the page and CSS (Cascading Style Sheets) that tell the browser how the content should be displayed in browsers and other user agents that need to display it. CSS tells the browser everything from the layout of the page to the colors of your headings."
CSS3 is the latest version of the CSS specification. The term "CSS3" is not just a reference to the new features in CSS, but the third level in the progress of the CSS specification. CSS3 contains just about everything that is included in CSS2.1 (the previous version of the specification). It also adds new features to help developers solve a number of problems without the need for non-semantic markup, complex scripting, or extra images.
Features that are included in CSS3 include support for additional selectors, drop shadows, rounded corners, multiple backgrounds, animation, transparency, and much more.