The development of CSS Level 3 (CSS3) started in 2005. In contrast to further CSS specifications, CSS3 is modularized. The CSS3 modules are described in separate specifications such as Selectors, Media Queries, Text, Backgrounds and Borders, Colors, 2D Transformations, 3D Transformations, Transitions, Animations, and Multi-Columns. The modules are in different stages of development and browser implementation. Until recently, only a few modules had been standardized, such as the
A variety of new functions and features have been introduced in CSS3 such as
; color declaration in HSL, HSLA, and RGBA;
; attribute selectors; transitions; multiple backgrounds; multicolumn layout; Web Fonts; and speech.
CSS3 is a superset of former CSS versions, and the core CSS properties can be used in any version, however, CSS3 introduced many new features and properties: