Connected blocks, add backdrop-color. (#65233)

Co-authored-by: jasmussen <joen@git.wordpress.org>
Co-authored-by: gziolo <gziolo@git.wordpress.org>
Co-authored-by: t-hamano <wildworks@git.wordpress.org>
Co-authored-by: mtias <matveb@git.wordpress.org>
Co-authored-by: jameskoster <jameskoster@git.wordpress.org>
Co-authored-by: SantosGuillamot <santosguillamot@git.wordpress.org>

packages/block-editor/src/components/block-toolbar/style.scss

@@ -37,6 +37,13 @@
 		border-right: $border-width solid $gray-300;
 	}
 
+	&.is-connected {
+		.block-editor-block-switcher .components-button::before {
+			background: color-mix(in srgb, var(--wp-block-synced-color) 10%, transparent);
+			border-radius: $radius-small;
+		}
+	}
+
 	&.is-synced,
 	&.is-connected {
 		.block-editor-block-switcher .components-button .block-editor-block-icon {