Add mixin for theming multiple properties at once

assets/stylesheets/shared/mixins/_custom-properties.scss

@@ -7,6 +7,9 @@
 // @include custom-property( color, --text-color, $text-color );
 // @include custom-property-from-map( color, --text-color, $text-color );
 // @include theme( color, --text-color );
+// @include theme-multiple(
+//   ('color': --text-color, 'background': --bg-color, 'border-color': --border-color);
+// )
 // ==========================================================================
 
 @mixin custom-property( $property, $custom-property, $fallback ) {
@@ -19,7 +22,13 @@
 	#{ $property }: var( $custom-property, map-deep-get( $map, $keys... ) );
 }
 
-// custom mixin for theming with custom properties based on $color-schemes map (see _themes.scss)
+// custom mixins for theming with custom properties based on $color-schemes map (see _themes.scss)
 @mixin theme( $property, $custom-property ) {
 	@include custom-property-from-map( $property, $custom-property, $color-schemes, 'default', $custom-property );
 }
+
+@mixin theme-multiple ($theme-properties) {
+	@each $property, $custom-property in $theme-properties {
+		@include theme( $property, $custom-property );
+	}
+}