z-index

The z-index CSS 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.

/* 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;

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.

The example above shows the effect of z-index. On the left we've drawn three boxes and made them overlap using absolute positioning. By default, the elements are stacked following the order they're declared in the HTML. On the right we have the same markup, but have reversed the default order using z-index.

Syntax

The z-index property is specified as either the keyword auto or an <integer>.

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

Browser compatibility

See also

• CSS position property
• Understanding CSS z-indexes