angular__angular/devtools/projects/ng-devtools/src/styles/_theme.scss

/* Keep class names in sync with ThemeService */
$dark-theme-class: 'dark-theme';
$light-theme-class: 'light-theme';

/* $browser expects 'chrome', 'firefox' or 'safari' */
@mixin _theme($theme, $browser: '') {
  @if $browser == '' {
    :host-context(:root.#{$theme}) {
      @content;
    }
  } @else {
    /* Keep browser class name in sync with BrowserService. */
    $browser-class: $browser + '-ui';
    :host-context(:root.#{$theme}.#{$browser-class}) {
      @content;
    }
  }
}

@mixin dark-theme($browser: '') {
  @include _theme($dark-theme-class, $browser) {
    @content;
  }
}

@mixin light-theme($browser: '') {
  @include _theme($light-theme-class, $browser) {
    @content;
  }
}