Custom CSS/SCSS for Blocks

Where can I add a custom CSS?

Site administration -> Appearane -> Monocolor -> Advanced -> Raw SCSS

/* Block #5 */
.rui-fp-block--5 {
	.rui-block-title {
		@include media-breakpoint-up(lg) {
		color: red;
		}
		
		@include media-breakpoint-only(md) {
		color: purple;
		}
				
		@include media-breakpoint-between(xs, sm) {
		color: blue;
		}
	}
}