Replace outdated colors with WikimediaUI palette ones

Replacing all colors with current WikimediaUI palette ones.
Also:
- changing two files over to LESS in order to
 - make use of central gradient mixin instead of one with
   unnecessary vendor extensions and
 - concatenating selectors in one occurrence.

Bug: T174237
Change-Id: I5d302f29b079f6abdba5abf3b58d6ba254e1a4ac

resources/css/ext.uls.less

@@ -47,7 +47,7 @@
 	display: block;
 	position: absolute;
 	left: 0;
-	border-right: 1px solid #c9c9c9;
+	border-right: 1px solid #c8ccd1;
 	opacity: 0.8;
 }