wp-calypso/client/assets/stylesheets/shared/mixins/_banner.scss

@mixin banner-color( $color ) {
	border-left-color: $color;

	.banner__icon {
		color: $color;
	}

	.banner__icon-circle {
		background-color: $color;
	}
}

@mixin banner-dark() {
	background-color: var(--color-neutral-70);

	.banner__list,
	.banner__title,
	.banner__description {
		color: #fff;
	}
}