CSS Positioning

CSS Positioning is a module of CSS that defines how to absolutely and relavitely position elements on the page.

Reference

CSS Properties

Guides

Understanding CSS z-index
Presents the notion of stacking context and explain how z-ordering works, with several examples.

Specifications

Specification Status Comment
CSS Positioned Layout Module Level 3 Рабочий черновик  
CSS Level 2 (Revision 1) Рекомендация