unity/resources/sass/user/components/bootstrap4/mixins/_badge.scss

@mixin badge-variant($bg) {
  color: color-yiq($bg);
  background-color: $bg;

  @at-root a#{&} {
    @include hover-focus {
      color: color-yiq($bg);
      background-color: darken($bg, 10%);
    }
  }
}