Replace outdated colors with WikimediaUI palette ones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.compactlinks.less

@@ -2,13 +2,11 @@
 @import 'ext.uls.mixins.less';
 
 /* stylelint-disable selector-no-id */
-
 #p-lang .body ul .uls-trigger,
 #p-lang .pBody ul .uls-trigger {
 	background-image: none;
 	padding: 0;
 }
-
 /* stylelint-enable selector-no-id */
 
 .mw-interlanguage-selector,
@@ -27,8 +25,8 @@
 
 .mw-interlanguage-selector:active,
 .mw-interlanguage-selector.selector-open {
-	color: #555;
-	background-color: #ccc;
+	background-color: #c8ccd1;
+	color: #54595d;
 }
 
 .interlanguage-uls-menu {