Cascading Style Sheets (CSS) is a style sheet language used to describe the look and formatting of a document written in a markup language, such as HTML and XHTML.
CSS3 is the most current specification and is split into modules. These modules give all the functionality of the previous specifications plus new features such as greater control over selectors, text effects, paged media, generated content and multi-column layouts which weren't considered possible until now.
The CSS specifications are maintained by the World Wide Web Consortium (W3C).