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Primer CSS offers multiple color themes for components and utilities. The colors change based on the active theme and color mode. When nothing is specified, Primer CSS uses the light theme.

Set a theme

Configure Primer CSS to use a certain theme by setting HTML attributes.

Themedata attributes
Lightdata-color-mode="light" data-light-theme="light"
Darkdata-color-mode="dark" data-dark-theme="dark"
Dark Dimmeddata-color-mode="dark" data-dark-theme="dark_dimmed"
Dark High Contrastdata-color-mode="dark" data-dark-theme="dark_high_contrast"

Typically these attributes are added to the document root (<html>) to use on the entire page:

<html data-color-mode="dark" data-dark-theme="dark_dimmed">

Below an example of all themes to compare:

Sync to the system

If the theme should be synced to the OS's color mode, use data-color-mode="auto" and set a data-light-theme as well as a data-dark-theme.

Change the color mode of your OS to see the switch between the data-light-theme="light" and data-dark-theme="dark_dimmed".

Custom color variables

It's recommended to use the functional variables as much as possible. It will guarantee that the variables will work as expected with any new theme that might get added in the future. Sometimes you might still need a custom variable that changes based on the color mode. You can create a custom variable with the color-variables mixin.

@include color-variables(
("custom-css-variable-1": (
light: var(--color-scale-gray-3),
dark: var(--color-scale-gray-5)
"custom-css-variable-2": (
light: var(--color-scale-gray-2),
dark: var(--color-scale-gray-6)
"custom-css-variable-3": (
light: var(--color-scale-gray-2),
dark: var(--color-scale-gray-6)

The custom variables will be prefixed with --color- and can be used in the same way as other functional variables.

.my-class {
color: var(--color-custom-css-variable-1);
background-color: var(--color-custom-css-variable-2);
border-color: var(--color-custom-css-variable-2);