Element.getClosestScrollableContainer: Use 'body' or 'documentElement' based on browser

Workaround for https://code.google.com/p/chromium/issues/detail?id=303131

Bug: T73609
Change-Id: I4ca3cb75090a68ddcd0baf345675c5011eb7444d
MediaWiki theme: Extract @active-color variable

Change-Id: Ibc5b586f86c853abec271b92506feae0e520c4ee
Merge "MediaWiki theme: Extract @active-color variable"
Merge "Element.getClosestScrollableContainer: Use 'body' or 'documentElement' based on browser"