In this article, we will cover css z-index and cover lots of use cases with code examples.

CSS Z-Index Complete Tutorial
CSS Z-Index Complete Tutorial

CSS z-index is a property that controls the vertical stacking order of elements on a web page.

This property can be used to control the order in which elements are displayed on top of each other, allowing web developers to create a more visually appealing layout.

In this article, we will explore the basics of the CSS z-index property, provide examples of its use cases, and give tips for its implementation.

Basics of the CSS z-index Property:

The z-index property in CSS determines the stacking order of positioned elements.

By default, all elements on a web page are positioned in the same plane, so their stacking order is determined by their order in the HTML markup.

However, when you apply the CSS z-index property to an element, it creates a new stacking context for that element and its descendants.

The z-index property takes a numeric value, which can be positive or negative.

The higher the value, the closer the element is to the top of the stack.

For example, an element with a z-index of 2 will be displayed on top of an element with a z-index of 1.

Example 1:

Let’s take a look at a simple example to understand the CSS z-index property better. Consider the following HTML and CSS code:

<!DOCTYPE html>
<html>
  <head>
    <style>
      #box1 {
        position: absolute;
        width: 200px;
        height: 200px;
        background-color: red;
        top: 50px;
        left: 50px;
        z-index: 1;
      }

      #box2 {
        position: absolute;
        width: 200px;
        height: 200px;
        background-color: blue;
        top: 100px;
        left: 100px;
        z-index: 2;
      }
    </style>
  </head>
  <body>
    <div id="box1"></div>
    <div id="box2"></div>
  </body>
</html>

In this example, we have two div elements with different z-index values.

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The first div element has a z-index of 1, and the second div element has a z-index of 2.

As a result, the blue box will be displayed on top of the red box because it has a higher z-index value.

Example 2:

Another example of the CSS z-index property can be seen in creating a modal window.

A modal window is a popup window that appears on top of the web page and is used to display information, such as a login form or a product details page.

To create a modal window, we can use the CSS z-index property to place the modal window on top of the rest of the web page content.

<!DOCTYPE html>
<html>
  <head>
    <style>
      #modal {
        position: fixed;
        top: 50%;
        left: 50%;
        transform: translate(-50%, -50%);
        background-color: white;
        width: 400px;
        height: 300px;
        z-index: 9999;
      }

      #overlay {
        position: fixed;
        top: 0;
        left: 0;
        right: 0;
        bottom: 0;
        background-color: rgba(0, 0, 0, 0.5);
        z-index: 9998;
      }
    </style>
  </head>
  <body>
    <div id="overlay"></div>
    <div id="modal">
      <h2>Modal Window</h2>
      <form>
        <label for="username">Username:</label>
        <input type="text" id="username"
 </form>
</div>
 </body>
</html>

In this example, we have two div elements: one for the modal window and one for the overlay.

The modal window is positioned in the center of the screen and has a higher z-index value than the overlay.

The overlay covers the entire web page and has a semi-transparent background color to create the effect of the rest of the web page is grayed out and inactive while the modal window is open.

Use Cases of CSS z-index Property:

In this section, we are going to look at 3 important use cases for the use of the z-index property. Each one of them is often used in most applications.

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1. Dropdown Menus

Dropdown menus are a common feature of many websites.

The CSS z-index property can be used to ensure that the dropdown menu appears on top of other content on the page, making it easier for users to select the desired option.

<!DOCTYPE html>
<html>
  <head>
    <style>
      .menu {
        position: relative;
        display: inline-block;
      }

      .menu ul {
        list-style: none;
        margin: 0;
        padding: 0;
        display: none;
        position: absolute;
        z-index: 999;
      }

      .menu:hover ul {
        display: block;
      }

      .menu li {
        background-color: white;
        padding: 10px;
        border-bottom: 1px solid black;
      }
    </style>
  </head>
  <body>
    <div class="menu">
      <a href="#">Menu</a>
      <ul>
        <li><a href="#">Option 1</a></li>
        <li><a href="#">Option 2</a></li>
        <li><a href="#">Option 3</a></li>
      </ul>
    </div>
  </body>
</html>

2. Modals

Modals are often used to display important information, such as login forms or product details pages.

The CSS z-index property can be used to ensure that the modal appears on top of other content on the page, making it more noticeable and easier to interact with.

<!DOCTYPE html>
<html>
  <head>
    <style>
      #modal {
        position: fixed;
        top: 50%;
        left: 50%;
        transform: translate(-50%, -50%);
        background-color: white;
        width: 400px;
        height: 300px;
        z-index: 9999;
      }

      #overlay {
        position: fixed;
        top: 0;
        left: 0;
        right: 0;
        bottom: 0;
        background-color: rgba(0, 0, 0, 0.5);
        z-index: 9998;
      }
    </style>
  </head>
  <body>
    <div id="overlay"></div>
    <div id="modal">
      <h2>Modal Window</h2>
      <form>
        <label for="username">Username:</label>
        <input type="text" id="username">
        <label for="password">Password:</label>
        <input type="password" id="password">
        <input type="submit" value="Login">
      </form>
    </div>
  </body>
</html>

3. Stacked Images

Stacking images can create an interesting visual effect on a web page.

The CSS z-index property can be used to control the order in which the images are displayed, allowing developers to create complex designs and layouts.

<!DOCTYPE html>
<html>
  <head>
    <style>
      img {
        position: absolute;
        width: 300px;
        height: 200px;
       .image1 {
         z-index: 3;
         top: 50px;
         left: 50px;
      }

  .image2 {
    z-index: 2;
    top: 100px;
    left: 100px;
  }

  .image3 {
    z-index: 1;
    top: 150px;
    left: 150px;
  }
</style>
</head>
  <body>
    <img class="image1" src="image1.jpg" alt="Image 1">
    <img class="image2" src="image2.jpg" alt="Image 2">
    <img class="image3" src="image3.jpg" alt="Image 3">
  </body>
</html>

In this example, we have three images that are positioned on top of each other using the position:absolute property.

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The z-index property is used to control the order in which the images are displayed.

The image with the highest z-index value (image1) appears on top, while the image with the lowest z-index value (image3) appears on the bottom.

Final Words

The CSS z-index property is a powerful tool for controlling the stacking order of elements on a web page.

By setting the z-index value of an element, developers can control whether the element appears in front of or behind other elements on the page.

This property can be used in a variety of ways, from creating dropdown menus and modals to stacking images and other visual elements.

By understanding how the z-index property works, developers can create complex layouts and designs that are visually appealing and easy to navigate.