How to Change a CSS Background Image’s Opacity

Introduction #

opacity is a CSS property that allows you to change the opaqueness of an element. By default, all elements have a value of 1. By changing this value closer to ``, the element will appear more and more transparent.
A common use case is using an image as part of the background. Adjusting the opacity can improve the legibility of text or achieve the desired appearance. However, there is no way to target the background-image of an element with opacity without affecting the child elements.
In this article, you will be presented with two methods to work around this limitation for background images with opacity.

Deploy your frontend applications from GitHub using DigitalOcean App Platform. Let DigitalOcean focus on scaling your app.

Prerequisites #

If you would like to follow along with this article, you will need:

Familiarity with opacity.
Familiarity with position: relative and position: absolute.
Familiarity with stacking context and z-index
Familiarity with the :before and :after pseudo-elements.

Method 1 — Using a Separate Image Element and Positioning #

The first approach will rely upon two elements. One is a “wrap” that provides a point of reference with position: relative. The second is an img element that appears behind the content with position: absolute and stacking context.
Here is an example of the markup for this approach:

<div class="demo-wrap">
  <img
    class="demo-bg"
    src="https://assets.digitalocean.com/labs/images/community_bg.png"
    alt=""
  >
  <div class="demo-content">
    <h1>Hello World!</h1>
  </div>
</div>

And here are the accompanying styles:

.demo-wrap {
  overflow: hidden;
  position: relative;
}

.demo-bg {
  opacity: 0.6;
  position: absolute;
  left: 0;
  top: 0;
  width: 100%;
  height: auto;
}

.demo-content {
  position: relative;
}

This markup and styles will produce a result with text on top of an image:

.css-bg-example-1 .demo-wrap {
overflow: hidden;
position: relative;
}

.css-bg-example-1 .demo-bg {
opacity: 0.6;
position: absolute;
left: 0;
top: 0;
width: 100%;
height: auto;
}

.css-bg-example-1 .demo-content {
position: relative;
}

.css-bg-example-1 .demo-content h1 {
padding-top: 100px;
padding-bottom: 100px;
padding-left: 1em;
padding-right: 1em;
}

Hello World!

The parent demo-wrap <div> establishes an absolute positioning containing block. The demo-bg <img> is set to position: absolute and assigned a slight opacity. The demo-content <div> is set to position: relative and due to how the markup is arranged it has a higher stacking context than demo-bg. It is also possible to use z-index for finer control over the stacking context.
There are some limitations to this approach. It assumes that your image is large enough to accomodate the size of any element. You may need to enforce size limitations to prevent an image from appearing cut off or not covering the entire height of an element. It will also require additional adjustments if you want to control the “background position” and no clean “background repeat” alternative.

Method 2 — Using CSS Pseudo-Elements #

The second approach will rely upon pseudo-elements. The :before and :after pseudo-elements are available to most elements. Typically, you would provide a content value and use it to append extra text at the beginning or end. However, it is also possible to provide an empty string and then you can utilize the pseudo-elements for designs.
Here is an example of the markup for this approach:

<div class="demo-wrap">
  <div class="demo-content">
    <h1>Hello World!</h1>
  </div>
</div>

And here are the accompanying styles:

.demo-wrap {
  position: relative;
}

.demo-wrap:before {
  content: ' ';
  display: block;
  position: absolute;
  left: 0;
  top: 0;
  width: 100%;
  height: 100%;
  opacity: 0.6;
  background-image: url('https://assets.digitalocean.com/labs/images/community_bg.png');
  background-repeat: no-repeat;
  background-position: 50% 0;
  background-size: cover;
}

.demo-content {
  position: relative;
}

This markup and styles will produce a result with text on top of an image:

.css-bg-example-2 .demo-wrap {
position: relative;
}

.css-bg-example-2 .demo-wrap:before {
content: ‘ ‘;
display: block;
position: absolute;
left: 0;
top: 0;
width: 100%;
height: 100%;
opacity: 0.6;
background-image: url(‘https://assets.digitalocean.com/labs/images/community_bg.png’);
background-repeat: no-repeat;
background-position: 50% 0;
background-size: cover;
}

.css-bg-example-2 .demo-content {
position: relative;
}

.css-bg-example-2 .demo-content h1 {
padding-top: 100px;
padding-bottom: 100px;
padding-left: 1em;
padding-right: 1em;
}

Hello World!

The parent demo-wrap <div> establishes an absolute positioning containing block. The pseudo-element :before is set to position: absolute, assigned a slight opacity, and uses background-size: cover to occupy all the available space.
This approach has the advantage of support for other background properties like background-position, background-repeat, and background-size. This approach has the disadvantage of using one of the pseudo-elements which may conflict with another design effect – like a clearfix solution.

Conclusion #

In this article, you learned about two methods to work around this limitation for background images with opacity.
If you’d like to learn more about CSS, check out our CSS topic page for exercises and programming projects.