Bootstrap/scss/mixins/_color-scheme.scss

// scss-docs-start mixin-color-scheme
@mixin color-scheme($name) {
  @if $name == dark {
    @media (prefers-color-scheme: dark) {
      @content;
    }
  } @else if $name == light {
    @media (prefers-color-scheme: light) {
      @content;
    }
  } @else {
    @media (prefers-color-scheme: #{$name}) {
      @content;
    }
  }
}
// scss-docs-end mixin-color-scheme