The CSS Z-Index Property

What is z-index?

Using the CSS z-index property, you can manipulate vertical stacking for overlapping elements:

img {         
   position: absolute;                
   z-index: -1;   
}

Note: if you worry about z-index not working, make sure to only use it for elements which have their position value defined as static.

CSS z-index property syntax

To define the z-index for an element, you need to specify one value:

z-index: value;

The default value is auto, which means the stacking level depends on the parent container.

To define a custom level, use a unitless number. Elements with higher values will cover the ones with smaller values.

Browser support

Mobile browser support