Dark Mode Theme

Guidance for adding a dark mode theme to your site


A dark mode theme for Modus Bootstrap is now available. You can preview how it looks with the sun/moon toggle to the right of the search input above.

How you choose to implement a dark-mode theme on your site is up to you but a few suggested options are suggested below:

Display the theme based on users browser preference

<link rel="stylesheet" href="/common-styles.css" />
<link rel="stylesheet" href="/modus.min.css" media="(prefers-color-scheme: light)" />
<link rel="stylesheet" href="/modus-dark.min.css" media="(prefers-color-scheme: dark)" />

This is the easiest method and doesn’t require any additional JavaScript but a user won’t be able to change their site’s color scheme preference from your site. The site theme will always match the users system/browser preference.

Use a theme-toggle JavaScript library

If you’d like to give users the ability to switch the theme from your site then you can load the CSS with something like:

html[data-theme="light"] {
  color-scheme: dark;
  @import "modus-bootstrap";
html[data-theme="dark"] {
  color-scheme: dark;
  @import "modus-bootstrap-dark";

and then use a custom JavaScript such as Theme Switch by Adam Argyle. We are using a modified version of that script for this site.


  • Avoid using color utility classes (e.g. .bg-dark, .bg-white, text-dark) in your HTML if the colors will be different between light and dark mode, instead define colors for dark and light modes in your CSS separately.
  • Be sure to thoroughly test your site in both light and dark mode. Test in multiple browsers and devices.
  • Consider using PurgeCSS to reduce the file-size of the CSS to improve CSS load times.

Note: In order to use modus-layout.css with dark-mode CSS the layout CSS should be loaded before so that the dark-mode CSS overrides other background-colors set.