Implementing dark mode with prefers-color-scheme

Adding a dark mode to your website is quick and easy with CSS and the prefers-color-scheme media feature.

I've just added dark mode support to my site and wanted to do a quick post to document it. As a first pass, using prefers-color-scheme is a really simple way to present visitors with a version of your site that is more aligned with their own viewing preferences.

I may later add a toggle option to allow visitors to switch between light and dark modes. But that's more work for what is essentially a nice-to-have. A visitor who prefers dark mode is unlikely to want to switch to the light version, and vice versa.

Which version are you seeing?

Well, the nice thing about prefers-color-scheme is that it's a user preference set at operating system level. Some browsers, like Firefox, also let you choose between a light and dark theme that will override the operating system preference.

So, if your operating system or browser is set to use a light theme, you'll be seeing this site with a white background and black text. If you've chosen a dark theme instead, my site will have a black background with white text.

Here's the code

I'm using CSS variables for my colours, so here's a simplified version showing how it works:

:root {
    --colorBackground: white;
    @media (prefers-color-scheme: dark) {
        --colorBackground: black;

The media feature prefers-color-scheme is available in all modern browsers. Check out MDN web docs for more information.

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