Fix sass warning during build

Author: electerious

src/ui/styles/_modal.scss

@@ -1,3 +1,5 @@
+@use 'sass:color';
+
 .modal {
 
 	position: fixed;
@@ -9,7 +11,7 @@
 	bottom: 0;
 	left: 0;
 	padding: 0 $gutter;
-	background: rgba(darken($black, 6%), .9);
+	background: rgba(color.adjust($black, $lightness: -6%), .9);
 	pointer-events: none;
 	opacity: 0;
 	z-index: 3;