Adapting to user motion and theme preferences with CSS and JavaScript

Written by Oscar Jite-Orimiono✏️

The internet is full of color, animations, and graphic effects that can make websites both captivating and overstimulating. As frontend enthusiasts and professionals, we need to balance vibrant visuals with accessible, user-centered options for those who prefer a more subdued experience.

In this article, we're going to do more with less by taking a look at the below items:

• Learn to use media queries like prefers-reduced-motion and prefers-color-scheme to manage animations and themes
• Follow correct syntax in @media rules to apply user preferences
• View options like prefers-reduced-data that will minimize data use for users with limited connectivity

Motion preferences

For many users, animations can enhance their experience on a website, but they may impede others. Too much motion can cause discomfort or be a distraction, plus it could cause performance issues.

The prefers-reduced-motion media query checks if a user has enabled settings on their computer to limit website animations. You can modify or completely disable animations for users who prefer reduced motion.

To get started, let's create a webpage with some animation. How about an animated striped background?

Here’s the HTML for the page:

<div class="container">
    <div class="content">
      <h1>User Preferences</h1>
      <p>prefers-reduced-motion</p>
    </div>
  </div>

And here’s the CSS:

.container {
  position: relative;
  width: 100%;
  height: 100%;

  &::before {
    position: absolute;
    content: "";
    top: 0;
    left: 0;
    height: 100%;
    width: calc(100% + 110px);
    background: repeating-linear-gradient(
      45deg,
      #553c9a 0%,
      #553c9a 25%,
      #301934 25%,
      #301934 50%
    );
    background-size: 110px 110px;
    animation: animateStripes 2s linear infinite;
  }
}
@keyframes animateStripes {
 to {
    transform: translateX(-110px);
  }
}

Here’s how it looks with the animated stripes:

The no-preference syntax is for users with no preference settings while reduce is for those who do. You can completely disable or modify animations for the users who prefer reduced motion. Here’s how to disable the moving background using the prefers-reduced-motion media query:

@media (prefers-reduced-motion: reduce) {
  .container::before {
    animation: none;
  }
}

Side note: On devices that run Windows 11, you can disable animations by going into Settings, selecting Accessibility, then Visual Effects, and toggling off Animation Effects. The process is similar for nearly every type of device/operating system.

Here’s a CodePen:

You can choose to change the type of animation instead of disabling them. For instance, instead of a slide-in transform animation, you use a fade-in animation for users who prefer reduced motion.

If you use scroll animations with elements sliding in from one side of the page, you can switch to a simpler effect, like a fade-in.

Here’s CSS for a simple scroll animation:

.box {
  transform: translateX(100%);
  opacity: 0;
  transition: transform 0.5s linear, opacity 0.5s linear;
}
.reveal {
  transform: translateX(0);
  opacity: 1;
}
@keyframes reveal {
  to {
    transform: translateX(0);
    opacity: 1;
  }
}

In this example, the box elements will fade in from the right side of the webpage and move towards the left. This movement is controlled by the transform property, so you can simply remove it for users who prefer reduced motion:

@media (prefers-reduced-motion: reduce) {
  .box {
    transform: translateX(0);
  }
}

Users with no-preference will see this when they scroll:

And here’s what users with reduce will see:

With the prefers-reduced-motion media query you can tone/slow down complex animations or disable them entirely based on what the user wants.

Here’s a CodePen to interact with where you can disable animations on your device to see the difference:

Users with vestibular disorders like motion sickness and vertigo may become disoriented or dizzy when looking at animations. Animations can also be distracting for users who prefer to have a simple UI.

Having the option of reduced motion will make websites much more comfortable to use for users sensitive to motion.

Theme preferences

It’s now common practice for websites and applications to have the option of switching from a light theme to a darker one. Some websites give you an extra option based on system preferences.

The prefers-color-scheme media query detects if a user prefers dark or light themes. The users can get a default theme based on their device settings.

Here’s a webpage with light colors:

This is what users will see if their default theme is light. You can then use the prefers-color-scheme to create the dark theme:

@media (prefers-color-scheme: dark) {
    #main {
    background-image: repeating-linear-gradient(
      45deg,
      #553c9a,
    #553c9a 50px,
    #3a1e4f 50px,
    #3a1e4f 100px,
    #301934 100px,
    #301934 150px
    );
  }
  nav{
    background: rgba(0, 0, 0, 0.5);
  }
  .logo a,
  nav ul li a{
    color: #b393d3;
  }
  .content {
    background: rgba(0, 0, 0, 0.5);
  }
  .content h1 {
    color: #b393d3;
  }
  .content p{
    color: #b393d3;
  }
}

Writing out the CSS rules like this for both light and dark modes might be too much work, especially when several properties share the same values. Using variables to map out the color schemes will help you avoid repetition:

:root {
  --bg-color: repeating-linear-gradient(
    45deg,
    #876a9e,
    #876a9e 50px,
    #b393d3 50px,
    #b393d3 100px,
    #a288b2 100px,
    #a288b2 150px
  );
  --nav-main-bg: rgba(255, 255, 255, 0.1);
  --text-color: #301934;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg-color: repeating-linear-gradient(
      45deg,
      #553c9a,
      #553c9a 50px,
      #3a1e4f 50px,
      #3a1e4f 100px,
      #301934 100px,
      #301934 150px
    );
    --nav-main-bg: rgba(0, 0, 0, 0.5);
    --text-color: #b393d3;
  }
}

Here’s a screenshot of the same page as before but with dark mode activated:

Here’s a CodePen you can interact with:

The prefers-color-scheme is not limited to colors only; you can use it to swap out images:

:root {
  --bg-image: url(/plufow-le-studio-bPEsxCiXFIU-unsplash.jpg);
  --nav-content-bg: rgba(255, 255, 255, 0.1);
  --text-color: #301934;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg-image: url(/plufow-le-studio-lFjIBTDlYuo-unsplash.jpg);
    --nav-content-bg: rgba(0, 0, 0, 0.5);
    --text-color: #b393d3;
  }
}

Here’s a screenshot of the webpage in light mode:

Background photo by Plufow Le Studio on Unsplash.

And here’s the page in dark mode:

[caption id="" align="aligncenter" width="1314"]
Background photo by Plufow Le Studio on Unsplash.

Best practices

Be sure to test color contrasts before using them to ensure better readability. There are several tools available that can help you pick the colors to use.

Consider every possible element that needs updating when switching themes, not just the background and text. This is why storing the themes using CSS variables is a good idea, you may need to provide alternates for buttons, shadows, borders, links, and more.

Implementation

The most straightforward way to implement user preferences is to use the @media rule. You must specify the preference for motion or themes, otherwise, the CSS rules inside the media query will override any other rules or device settings.

This means that for motion preferences, you must specify if it’s reduce or no-preference, and for themes, it’s light or dark:

/* Wrong */
@media (prefers-reduced-motion)
@media (prefers-color-scheme)

/* Correct */
@media (prefers-reduced-motion: reduce)
@media (prefers-reduced-motion: no-preference)

@media (prefers-color-scheme: dark)
@media (prefers-color-scheme: light)

This can be useful when testing your code, but be sure to specify the exact preference before implementation.

Implementing user preferences with JavaScript

User preferences can also be implemented with JavaScript. You can add a new class to specific elements based on user preferences.

Using our first example with the animated stripes, here’s how to check for user preferences with JavaScript:

const stripes = document.querySelector('.container');
if (window.matchMedia('(prefers-reduced-motion: reduce)').matches) {
  stripes.classList.add('reduced-motion');
} else{
  stripes.classList.remove('reduced-motion');
}

Here’s the CSS:

.container.reduced-motion::before {
  animation: none;
}

Note that pseudo-elements are not part of the DOM and can’t be directly selected in JavaScript, hence this approach.

Implementing user preferences with data attributes

Custom HTML data attributes and JavaScript allow you to implement user preferences. Data attributes allow you to store information on HTML elements without affecting the document's structure. They use the data prefix and can be easily manipulated using JavaScript:

 const containers = document.querySelectorAll('.container');
    // update animations based on user preference
    function updateAnimationPreference() {
      if (window.matchMedia('(prefers-reduced-motion: reduce)').matches) {
        // remove attribute if user prefers reduced motion
        containers.forEach((stripes) => {
          stripes.removeAttribute("data-animated");
        });
      } else {
        // add attribute if there's no preference
        containers.forEach((stripes) => {
          stripes.setAttribute("data-animated", "true");
        });
      }
    }
    updateAnimationPreference();
    // Listen for changes to motion settings
    window.matchMedia('(prefers-reduced-motion: reduce)').addEventListener('change', updateAnimationPreference)

Here’s the CSS:

.container::before {
  animation: none;
}
.container[data-animated="true"]::before {
  animation: animateStripes 2s linear infinite;
}
@keyframes animateStripes {
  to {
    transform: translateX(-110px);
  }
}

Reduced data usage

While still experimental, prefers-reduced-data is a proposed media query that allows websites to detect if users prefer to save data.

It uses the same syntax as the prefers-reduced-motion media query, which is reduce for users who prefer lightweight content and no-preference for users with no data preference.

Some of its potential applications include reducing high-resolution images, loading alternate fonts, disabling autoplay videos, and lazy-loading non-critical content. This media query could help improve load times for users on limited or costly data plans, or with unreliable internet connections.

Final words

Respecting user preferences is crucial for enhancing every user's experience. In this tutorial, you learned how to use the prefers-reduced-motion and prefers-color-scheme media query to detect a user’s motion and theme settings. There are also @media rules for contrast and transparency preferences.

As a web developer, you’re the architect with the power to make every website comfortable, accessible, and efficient for every type of user.

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