Rivington: Clean up dim support in cover block.

rivington/style-rtl.css

@@ -1516,6 +1516,12 @@ button[data-load-more-btn], .button {
 	 */
 }
 
+.wp-block-cover.has-background-dim,
+.wp-block-cover-image.has-background-dim {
+	background-color: black;
+	color: white;
+}
+
 .wp-block-cover .wp-block-cover__inner-container,
 .wp-block-cover .wp-block-cover-image-text,
 .wp-block-cover .wp-block-cover-text,
@@ -2461,6 +2467,7 @@ table.is-style-stripes tbody tr:nth-child(odd),
 	background-color: #EE4266;
 }
 
+.has-background-dim,
 .has-foreground-background-color,
 .has-foreground-background-color.has-background-dim {
 	background-color: #f2f2f2;