light-dark() CSS function

The light-dark() CSS function accepts two colors or two images and returns a color or an image based on the active color scheme, without needing a prefers-color-scheme media feature.

Syntax

css
/* Named color values */
light-dark(
  black,
  white
);

/* RGB color values */
light-dark(
  rgb(0 0 0),
  rgb(255 255 255)
);

/* image url values */
light-dark(
  url("light-icon.png"),
  url("dark-icon.png")
);

/* linear-gradient values */
light-dark(
  linear-gradient(135deg, ghostwhite 20%, tomato),
  linear-gradient(45deg, darkslategray 20%, gold)
);

/* Custom properties */
light-dark(
  var(--light),
  var(--dark)
);

Values

The light-dark() function has two forms:

Description

Users can indicate their color scheme preference through their operating system settings (e.g., light or dark mode) or their user agent settings. The light-dark() function enables providing either two color values where any <color> value is accepted or two image values where any <image> value is accepted. The light-dark() function returns the first value if the used color scheme is light or if no preference is set and the second value if the used color scheme is dark.

To enable support for the light-dark() color function, the color-scheme must have a value of light dark, usually set on the :root pseudo-class.

css
:root {
  color-scheme: light dark;
}
body {
  color: light-dark(#333b3c, #efefec);
  background-color: light-dark(#efedea, #223a2c);
}

Formal syntax

<light-dark()> = 
  <light-dark-color>  |
  <light-dark-image>  

<light-dark-color> = 
  light-dark( <color> , <color> )  

<light-dark-image> = 
  light-dark( [ <image> | none ] , [ <image> | none ] )  

<image> = 
  <url>           |
  <image()>       |
  <image-set()>   |
  <cross-fade()>  |
  <element()>     |
  <gradient>      

<image()> = 
  image( <image-tags>? [ <image-src>? , <color>? ]! )  

<image-set()> = 
  image-set( <image-set-option># )  

<cross-fade()> = 
  cross-fade( <cf-image># )  

<element()> = 
  element( <id-selector> )  

<image-tags> = 
  ltr  |
  rtl  

<image-src> = 
  <url>     |
  <string>  

<image-set-option> = 
  [ <image> | <string> ] [ <resolution> || type( <string> ) ]?  

<cf-image> = 
  [ <image> | <color> ]  &&
  <percentage [0,100]>?  

<id-selector> = 
  <hash-token>

Examples

undefined

Setting colors based on a color scheme

By default, in supporting browsers, the color returned by the light-dark() color function depends on the user preference set through an operating system's settings (e.g., light or dark mode) or from a user agent setting. You can also change this setting in the browser's developer tools.

HTML

We include three sections to enable targeting light colors, dark colors, and the colors selected based on the user's preferred color scheme.

html
<h1><code>light-dark()</code> CSS function</h1>
<section>
  <h2>Automatic</h2>
  <p>This section will react to the users system or user agent setting.</p>
</section>
<section class="light">
  <h2>Light</h2>
  <p>
    This section will be light due to the <code>color-scheme: light;</code>.
  </p>
</section>
<section class="dark">
  <h2>Dark</h2>
  <p>This section will be dark due to the <code>color-scheme: dark;</code>.</p>
</section>

CSS

We include colors for both light and dark themes. We also define color-scheme for the document on the :root to enable the light-dark() color function for the entire document.

css
:root {
  /* this has to be set to switch between light or dark */
  color-scheme: light dark;

  --light-bg: ghostwhite;
  --light-color: darkslategray;
  --light-code: tomato;

  --dark-bg: darkslategray;
  --dark-color: ghostwhite;
  --dark-code: gold;
}
* {
  background-color: light-dark(var(--light-bg), var(--dark-bg));
  color: light-dark(var(--light-color), var(--dark-color));
}
code {
  color: light-dark(var(--light-code), var(--dark-code));
}

In addition to enabling the light-dark() function, the color-scheme property enables overriding a user's color scheme for document sections. Forcing a page section to only use a light or dark color scheme can be done by setting the color-scheme property to light or dark.

Note: Generally this should not be done, we are using it here for demonstration purposes. If the user has made a preference, you generally should not override their preferences.

css
.light {
  /* forces light color-scheme */
  color-scheme: light;
}
.dark {
  /* forces dark color-scheme */
  color-scheme: dark;
}

Result

Setting gradient background based on a color scheme

This example uses the same HTML code as the previous example but includes a <div> instead of a <p>.

CSS

Firstly, we define light and dark linear-gradient() values as custom properties.

css
:root {
  /*  light dark gradients  */
  --light-grad: linear-gradient(135deg, var(--light-bg) 20%, var(--light-code));
  --dark-grad: linear-gradient(45deg, var(--dark-bg) 30%, var(--dark-code));
}

Then we use the custom properties with light-dark() to set the background-image property based on the active color scheme.

css
section div {
  background-image: light-dark(
    var(--light-grad),
    var(--dark-grad)
  );
}

Result

Specifications

See also