Using z-index
The first article of this guide,Stacking without thez-index property, explains how stacking is arranged by default. If you want to create a custom stacking order, you can use thez-index property on apositioned element.
Thez-index property can be specified with an integer value (positive, zero, or negative), which represents the position of the element along an imaginary z-axis. If you are not familiar with the term 'z-axis', imagine the page as a stack of layers, each one having a number. Layers are rendered in numerical order, with larger numbers above smaller numbers (X represents an arbitrary positive integer):
| Layer | Description |
|---|---|
| Bottom layer | Farthest from the observer |
| Layer -X | Layers with negativez-index values |
| Layer 0 | Default rendering layer |
| Layer X | Layers with positivez-index values |
| Top layer | Closest to the observer |
Note:
- When no
z-indexproperty is specified, elements are rendered on the default rendering layer (Layer 0). - If several elements share the same
z-indexvalue (i.e., they are placed on the same layer), stacking rules explained in the sectionStacking without thez-indexproperty apply.
Example
In this example, the layers' stacking order is rearranged usingz-index. Thez-index of DIV #5 has no effect since it is not a positioned element.
HTML
<div> <strong>DIV #1</strong> <br />position: absolute; <br />z-index: 5;</div><div> <strong>DIV #2</strong> <br />position: relative; <br />z-index: 3;</div><div> <strong>DIV #3</strong> <br />position: relative; <br />z-index: 2;</div><div> <strong>DIV #4</strong> <br />position: absolute; <br />z-index: 1;</div><div> <strong>DIV #5</strong> <br />no positioning <br />z-index: 8;</div>CSS
div { padding: 10px; opacity: 0.7; text-align: center;}strong { font-family: sans-serif;}#abs1 { z-index: 5; position: absolute; width: 150px; height: 350px; top: 10px; left: 10px; border: 1px dashed #990000; background-color: #ffdddd;}#rel1 { z-index: 3; height: 100px; position: relative; top: 30px; border: 1px dashed #669966; background-color: #ccffcc; margin: 0px 50px;}#rel2 { z-index: 2; height: 100px; position: relative; top: 15px; left: 20px; border: 1px dashed #669966; background-color: #ccffcc; margin: 0px 50px;}#abs2 { z-index: 1; position: absolute; width: 150px; height: 350px; top: 10px; right: 10px; border: 1px dashed #990000; background-color: #ffdddd;}#sta1 { z-index: 8; height: 70px; border: 1px dashed #999966; background-color: #ffffcc; margin: 0px 50px;}