themes-wordpress/quadrat/sass/block-styles/_cover.scss

.wp-block-cover.is-style-quadrat-cover-diamond {

	&::after {
		background-image: url(rotated.svg);
		background-position: center;
		background-repeat: no-repeat;
		background-size: auto 70%;
		content: "";
		mix-blend-mode: soft-light;
		position: absolute;
		top: 0;
		left: 0;
		bottom: 0;
		right: 0;
		z-index: 0 !important; 
	}

	&.has-white-background-color,
	&.has-black-background-color {

		&.wp-block-cover.has-background-dim:not(.has-background-gradient)::before {
			opacity: 0;
		}

		&::after {
			mix-blend-mode: normal;
			mask-image: url(rotated.svg);
			mask-repeat: no-repeat;
			mask-size: auto 70%;
			mask-position: center;
			opacity: 0.25;
		}
	}

	&.has-white-background-color::after {
		background: #000;
	}

	&.has-black-background-color::after {
		background: #fff;
	}
}