What is CSS and the use of webdesign?

CSS Cascading Style Sheets is a style sheet language used for describing the presentation semantics (the look and formatting) of a document written in a markup language. Its designed primarily to enable the separation of document content (written in HTML or a similar markup language) from document presentation, including elements such as the layout, colors, and fonts.

CSS3

CSS3 is the latest standard for CSS. It is divided into several separate documents called "modules". Each module adds new capabilities or extends features defined in CSS 2, over preserving backward compatibility. Work on CSS level 3 started around the time of publication of the original CSS 2 recommendation.

CSS4

 W3C started drafting CSS4 However, it is currently not supported by any major web browser.