Summary

The z-index property specifies the z-order of an element and its descendants. When elements overlap, z-order determines which one covers the other. An element with a larger z-index generally covers an element with a lower one.

For a positioned box, the z-index property specifies:

  1. The stack level of the box in the current stacking context.
  2. Whether the box establishes a local stacking context.

Syntax

/* Keyword value */
z-index: auto;

/* <integer> values */
z-index: 0;
z-index: 3;
z-index: 289;
z-index: -1; /* Negative values to lower the priority */

/* Global values */
z-index: inherit;
z-index: initial;
z-index: unset;

Values

auto
The box does not establish a new local stacking context. The stack level of the generated box in the current stacking context is the same as its parent's box.
<integer>
This integer is the stack level of the generated box in the current stacking context. The box also establishes a local stacking context in which its stack level is 0. This means that the z-indexes of descendants are not compared to the z-indexes of elements outside this element.

Formal syntax

auto | <integer>

Examples

HTML

<div class="dashed-box">Dashed box
  <span class="gold-box">Gold box</span>
  <span class="green-box">Green box</span>
</div>

CSS

.dashed-box { 
  position: relative;
  z-index: 1;
  border: dashed;
  height: 8em;
  margin-bottom: 1em;
  margin-top: 2em;
}
.gold-box { 
  position: absolute;
  z-index: 3; /* put .gold-box above .green-box and .dashed-box */
  background: gold;
  width: 80%;
  left: 60px;
  top: 3em;
}
.green-box { 
  position: absolute;
  z-index: 2; /* put .green-box above .dashed-box */
  background: lightgreen;
  width: 20%;
  left: 20em;
  top: -25px;
  height: 7em;
  opacity: 0.9;
}

Result

 

Specifications

Specification Status Comment
CSS Transitions
The definition of 'animation behavior for z-index' in that specification.
Working Draft Defines z-index as animatable.
CSS Level 2 (Revision 1)
The definition of 'z-index' in that specification.
Recommendation Initial specification.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support 1.0 1.0 (1.7 or earlier) 4.0 4.0 1.0
Negative values (CSS2.1 behavior, not allowed in the obsolete CSS2 spec) 1.0 3.0 (1.9) 4.0 4.0 1.0
Feature Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support ? ? ? ? ?

See also

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