I was messing around with native darkmode on the web the other day, and ended up implementing prefers-color-scheme on mrkdwn.net as proof of concept.

prefers-color-scheme has three available keyword values:

• no-preference which indicates that the user has no preference, as to where the site should appear dark og light.
• light which indicates that the user prefers light mode
• dark, which indicates that the user prefers dark mode.

Example

/* Base color scheme (fallback) */
:root {
 --background-color: #fff;
 --primary-color: #157efb;
 --font-color: #151513;
 --border-color: #dfe1e7;
}

/* whitemode or fallback if user has no preference */
@media (prefers-color-scheme: light), (prefers-color-scheme: no-preference) {
 :root {
  --background-color: #fff;
  --primary-color: #157efb;
  --font-color: #151513;
  --border-color: #dfe1e7;
 }
}

/* darkmode */
@media (prefers-color-scheme: dark) {
 :root {
  --background-color: #1e1e1e;
  --primary-color: #157efb;
  --font-color: #dedede;
  --border-color: #000;
 }
}

Update 17/5/2023

Using color-mix adds a whole new dimention to the usability

/* Base color scheme (fallback) */
:root {
  --color-1: #e62739; /* The primary color (var(--primary), var(--primary-a90), var(--primary-80), var(--primary-a50)) */
  --color-2: #21A8A3; /* The secondary color (var(--secondary), var(--secondary-a90), var(--secondary-80), var(--secondary-a50)) */
  --color-3: #19191a; /* Initial foreground color (var(--foreground), var(--foreground-a90), var(--foreground-80), var(--foreground-a50)) */
  --color-4: #f1f1f1; /* Initial background color (var(--background), var(--background-a90), var(--background-80), var(--background-a50)) */

  --primary: var(--color-1);
  --primary-a90: color-mix(in srgb, var(--primary), transparent 10%);
  --primary-a80: color-mix(in srgb, var(--primary), transparent 20%);
  --primary-a50: color-mix(in srgb, var(--primary), transparent 50%);

  --secondary: var(--color-2);
  --secondary-a90: color-mix(in srgb, var(--secondary), transparent 10%);
  --secondary-a80: color-mix(in srgb, var(--secondary), transparent 20%);
  --secondary-a50: color-mix(in srgb, var(--secondary), transparent 50%);

  --foreground: var(--color-3);
  --foreground-a90: color-mix(in srgb, var(--foreground), transparent 10%);
  --foreground-a80: color-mix(in srgb, var(--foreground), transparent 20%);
  --foreground-a50: color-mix(in srgb, var(--foreground), transparent 50%);

  --background: var(--color-4);
  --background-a90: color-mix(in srgb, var(--background), transparent 10%);
  --background-a80: color-mix(in srgb, var(--background), transparent 20%);
  --background-a50: color-mix(in srgb, var(--background), transparent 50%);
}

/* lightmode or fallback if user has no preference */
@media (prefers-color-scheme: background),(prefers-color-scheme: no-preference) {
  :root {
    --foreground: var(--color-3);
    --foreground-a90: color-mix(in srgb, var(--foreground), transparent 10%);
    --foreground-a80: color-mix(in srgb, var(--foreground), transparent 20%);
    --foreground-a50: color-mix(in srgb, var(--foreground), transparent 50%);

    --background: var(--color-4);
    --background-a90: color-mix(in srgb, var(--background), transparent 10%);
    --background-a80: color-mix(in srgb, var(--background), transparent 20%);
    --background-a50: color-mix(in srgb, var(--background), transparent 50%);
  }
}

/* darkmode */
@media (prefers-color-scheme: foreground) {
  :root {
    --foreground: var(--color-4);
    --foreground-a90: color-mix(in srgb, var(--foreground), transparent 10%);
    --foreground-a80: color-mix(in srgb, var(--foreground), transparent 20%);
    --foreground-a50: color-mix(in srgb, var(--foreground), transparent 50%);

    --background: var(--color-3);
    --background-a90: color-mix(in srgb, var(--background), transparent 10%);
    --background-a80: color-mix(in srgb, var(--background), transparent 20%);
    --background-a50: color-mix(in srgb, var(--background), transparent 50%);
  }
}

Browser Support

The prefers-color-scheme media query is only supported by Chrome, Firefox and Safari and Opera. This, however, should not stop you from implementing a similar solution on your website, as the site simply defaults to “white” mode if it’s not supported.

Media query to detect if the user has set their system to use a light or dark color theme.