CSS3 is the latest standard of CSS earlier versions (CSS2). Cascading Style Sheets, level 1 (CSS1) was came out of W3C as a recommendation in December 1996. This version describes the CSS language as well as a simple visual formatting model for all the HTML tags.
CSS2 became a W3C recommendation in May 1998 and builds on CSS1. This version adds support for media-specific style sheets e.g. printers and aural devices, downloadable fonts, element positioning, and tables.
CSS3 became a W3C recommendation in June 1999 and builds on older versions CSS. It has divided into documentation is called as Modules and here each module having new extension features defined in CSS2.