---
title: Z Index
---
## Z Index
Z Index (`z-index`) is a CSS property that defines the order of overlapping HTML elements. Elements with a higher index will be placed on top of elements with a lower index.
**Note**: Z index only works on positioned elements (`position:absolute`, `position:relative`, or `position:fixed`).
#### Possible Values
```css
/* Default value if not specified */
z-index: auto;
/* Integer values */
z-index: 1;
z-index: 100;
z-index: 9999;
z-index: -1;
/* Global values */
z-index: inherit;
z-index: initial;
z-index: unset;
```
#### Example Usage
In this example, you can see three boxes displayed on top of each other in different orders using `z-index`.
HTML
```html
```
CSS
```css
#blue {
background-color: blue;
}
#red {
background-color: red;
}
#green {
background-color: green;
}
```
Since `z-index` wasn't defined, it will have a default value of `auto`. This is a result:
![An image of three boxes](https://image.prntscr.com/image/Yc9oGkdKTnm_YIHzaKQmbQ.png)
Try to change the order to Green, Blue, Red in CSS using `z-index`.
```css
#blue {
background-color: blue;
z-index: 2;
}
#red {
background-color: red;
z-index: 1;
}
#green {
background-color: green;
z-index: 3;
}
```
Your result will be:
![An image of three boxes](https://image.prntscr.com/image/Am9XxPO4Q2mq-PcokJ47Wg.png)
Use Z Index if you need to put a background element below a container. You can easily place the background under every element by giving it a negative Z Index like below:
```css
#background {
z-index: -1;
}
```
#### More Information:
https://css-tricks.com/almanac/properties/z/z-index/
https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Positioning/Understanding_z_index
https://philipwalton.com/articles/what-no-one-told-you-about-z-index/