z-index

Summary

The z-index CSS 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.

• Initial value auto
• Applies to positioned elements
• Inherited no
• Media visual
• Computed value as specified
• Animatable yes, as an integer
• Canonical order the unique non-ambiguous order defined by the formal grammar

Syntax

Formal syntax: auto | <integer>

z-index: auto     /* Keyword value */
z-index: 0        /* <integer> value */
z-index: 3
z-index: 289

z-index: inherit

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.

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: 2;
  background: gold;
  width: 80%;
  left: 60px;
  top: 3em;
}
.green-box { 
  position: absolute;
  z-index: 3;
  background: lightgreen;
  width: 20%;
  left: 20em;
  top: -25px;
  height: 7em;
  opacity: 0.9;
}

Result

Specifications

Browser compatibility

See also

• CSS position property
• Understanding CSS z-indexes