[Frontend] Form styling

#772
Added ".l-controls-under" styling to allow
channel-selector layout;
Added new hint color constants and refined
style defs;

platform/commonUI/general/res/sass/overlay/_overlay.scss

@@ -65,9 +65,7 @@
         margin-bottom: $interiorMargin;
     }
 
-    .hint {
-        color: pushBack($colorOvrFg, 20%);
-    }
+    .hint, .field-hints { color: $colorFieldHintOverlay !important;  }
 
     .abs.top-bar {
         height: $ovrTopBarH;