Improve unstyled updatedmarker

This is the "changed since your last visit" marker that you'll
see on ?action=history for a page on your watchlist, marking
edits that were made since you last viewed the page.
updatedmarker is styled by some skins, but not all of them.
Updating CSS selector and involved colors to address some of the concerns
and improving consistency.

Bug: T134515
Change-Id: Ib21ee453f0fa71fc8f516db1fec71096d962d194