Summary

The z-index property specifies the z-order of a positioned 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 (that is, one with any position other than static), 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.

Initial valueauto
Applies topositioned elements
Inheritedno
Mediavisual
Computed valueas specified
Animation typean integer
Canonical orderthe unique non-ambiguous order defined by the formal grammar
Creates stacking contextyes

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: 65%;
  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 definition

Browser compatibility

     
Feature Chrome Edge Firefox (Gecko) Internet Explorer Opera Safari
Basic support 1.0(Yes) 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 Edge Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support ?(Yes) ? ? ? ?
Negative values (CSS2.1 behavior, not allowed in the obsolete CSS2 spec) ?? ? ? ? ?

See also