CSS Full Form is Cascading Style Sheets. It is a language developed in 1997 to define the feel and look of web pages. This was to help the web developers to separate designs and contents so that HTML can perform its functions better. Though it was invented in 1997, it gained its popularity only from 2000. This was when various web browsers started using CSS to a greater extent.
Currently, almost all modern web browsers support CSS. This includes all of level 1 CSS, few of level 2 CSS and certain aspects of the level 3 CSS. In the name CSS or cascading style sheets, ‘style sheets’ refer to the documents. For several years, document designs have been using CSS. The term ‘cascade’ is used because; the web style sheets are supposed to cascade or pass through several style sheets for the desired effect.