If you’ve ever struggled to create a dropdown menu or sticky header that stays in front of other content, you’ll need to master the CSS z-index property. This simple yet powerful tool determines the stacking order of elements, influencing the visual hierarchy of your web page.

Delve into the basics and workings of the z-index property, and explore ways you may practically include it in your next web project.

Three boxes in different colors arranged from top to bottom on the left side of a page, the last box overlapping the second box.

What Is CSS z-index?

The CSS z-index property specifies the stacking order of overlapping elements on a web page. you’re able to use it to determine which elements appear in front or behind others.

Imagine a stack of colored papers that represent different elements on a web page. By assigning a number, you can influence the position of each paper in the stack. When you use z-index, a lower number means the element appears behind others, while a higher number means it’s in front.

Three boxes in different colors overlapping on one another in the order Red, Blue, and Green

The term z-index comes from the z-axis, representing the third dimension in a 3D Cartesian coordinate system. Z-axis indicates the depth of the object or how far back or forward it is within your line of sight.

How the CSS z-index Property Works

Thez-indexproperty has a simple syntax. Here are some examples:

The default value isautowhich, in most cases, is the same as a value of0. Note that you can use negative numbers which behave in the same way as positive numbers: lower values appear behind higher values in the stacking order.

You’ll need to learn how the CSS position property works to use the z-index property. Before applying z-index to an element, you must set its position property. Z-index works with any non-static element, which these common values of the position property all establish:

Google drive installer popup on a Blue textured desktop wallpaper.

Below is a simple example of z-index in action using one of the CSS position properties.

In this example, each colored box has a fixed position, defined with top and left. The z-index property controls the stacking order of boxes, with higher values bringing those elements to the front.

By experimenting with different position properties and values, you can explore the various ways to use z-index in your projects.

Practical Examples Using z-index

Here are some examples of web components using the z-index properties you can practice with.

These practical examples show the versatility of the z-index property in improving the visual layout and user experience on a web page.