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@media.prefers-color-scheme

If you have set privacy.resistFingerprinting to true, prefers-color-scheme preference is overridden to light.
Alternately, users can create the numeric preference ui.systemUsesDarkTheme to override the default behavior and return light (value: 0), dark (value: 1), or no-preference (value: 2). (Any other value causes Firefox to return light.)

The prefers-color-scheme CSS media feature is used to detect if the user has requested the system use a light or dark color theme.

Syntax

light: Indicates that user has notified the system that they prefer an interface that has a light theme, or has not expressed an active preference.
dark: Indicates that user has notified the system that they prefer an interface that has a dark theme.

Examples

The elements below have an initial color theme. They can be further themed according to the user's color scheme preference.

HTML

<div class="day">Day (initial)</div>
<div class="day light-scheme">Day (changes in light scheme)</div>
<div class="day dark-scheme">Day (changes in dark scheme)</div> <br>

<div class="night">Night (initial)</div>
<div class="night light-scheme">Night (changes in light scheme)</div>
<div class="night dark-scheme">Night (changes in dark scheme)</div>

CSS

.day   { background: #eee; color: black; }
.night { background: #333; color: white; }

@media (prefers-color-scheme: dark) {
  .day.dark-scheme   { background:  #333; color: white; }
  .night.dark-scheme { background: black; color:  #ddd; }
}

@media (prefers-color-scheme: light) {
  .day.light-scheme   { background: white; color:  #555; }
  .night.light-scheme { background:  #eee; color: black; }
}

.day, .night {
  display: inline-block;
  padding: 1em;
  width: 7em;
  height: 2em;
  vertical-align: middle;
}

Result

Specifications

Specification	Status	Comment
Media Queries Level 5 The definition of 'prefers-color-scheme' in that specification.	Editor's Draft	Initial definition.

Browser compatibilityUpdate compatibility data on GitHub

	Desktop
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari
`prefers-color-scheme` media feature	76	79	67	No	62	12.1
`no-preference` value	76 — 80	79 — 80	67 — 79	No	62 — 71	12.1

	Mobile
	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`prefers-color-scheme` media feature	76	76	No	54	13	12.0
`no-preference` value	76 — 80	76 — 80	67 — 79	54	13	12.0 — 13.0