How to Make the CSS z-index Property Work

Solutions with the CSS position property

The CSS z-index property only works with the position property. The position value must be other than static (i.e. absolute, relative, fixed, sticky).

Let’s see some examples.

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For regular positioning, use the "relative" value on the elements, on which you’ve also set the z-index property. Otherwise, there won’t be any effect.

Example of using the z-index property with the "relative" value of the position property:

<!DOCTYPE html>
<html>
  <head>
    <title>Title of the document</title>
    <style>
      div {
        width: 150px;
        height: 150px;
        padding: 15px;
      }
      .one,
      .two,
      .three {
        position: relative;
      }
      .one {
        background: #a7b5aa;
        outline: 2px solid #000;
        top: 100px;
        left: 200px;
        z-index: 10;
      }
      .two {
        background: #4b48db;
        outline: 2px solid #000;
        top: 50px;
        left: 75px;
        z-index: 100;
      }
      .three {
        background: #1ba13f;
        outline: 2px solid #000;
        top: 30px;
        left: 25px;
        z-index: 150;
      }
    </style>
  </head>
  <body>
    <div class="one"></div>
    <div class="two"></div>
    <div class="three"></div>
  </body>
</html>

Result

Example of using the z-index property with the "absolute" value of the position property:

<!DOCTYPE html>
<html>
  <head>
    <title>Title of the document</title>
    <style>
      img {
        position: absolute;
        left: 0;
        top: 20px;
        z-index: -1;
      }
    </style>
  </head>
  <body>
    <h2>Example</h2>
    <img src="/build/images/w3docs-logo-black.png" alt="W3docs logo" width="195" height="45">
  </body>
</html>

Now, let’s see how these boxes will behave with the "fixed" value.

Example of using the z-index property with the "fixed" value of the position property:

<!DOCTYPE html>
<html>
  <head>
    <title>Title of the document</title>
    <style>
      div {
        width: 150px;
        height: 150px;
        padding: 15px;
      }
      .one,
      .two,
      .three {
        position: fixed;
      }
      .one {
        background: #a7b5aa;
        outline: 2px solid #000;
        top: 100px;
        left: 200px;
        z-index: 10;
      }
      .two {
        background: #4b48db;
        outline: 2px solid #000;
        top: 50px;
        left: 75px;
        z-index: 100;
      }
      .three {
        background: #1ba13f;
        outline: 2px solid #000;
        top: 30px;
        left: 25px;
        z-index: 150;
      }
    </style>
  </head>
  <body>
    <div class="one"></div>
    <div class="two"></div>
    <div class="three"></div>
  </body>
</html>

When the z-index property is not applied, the browser stacks elements in the following default order:

  1. root element,
  2. non-positioned elements in the order they are specified,
  3. positioned elements in the order they are specified.