CSS positioned layout

The CSS positioned layout module defines how to position elements on a web page.

Reference

Properties

Selectors

Guides

Understanding z-index

Presents the notion of stacking context and explains how z-ordering works, with several examples.

Stacking without the z-index property

The stacking rules that apply when z-index is not used.

Stacking floating elements

How floating elements are handled with stacking.

Using z-index

How to use z-index to change default stacking.

Stacking context

CSS stacking context, the CSS features that create new stacking contexts, and nested stacking contexts.

Specifications

Specification
CSS Positioned Layout Module Level 3
CSS Positioned Layout Module Level 4