Fix FOUC for floated collapsible elements outside the content area

There was CSS setting the correct float value, but it only worked on
elements inside the content area because it used .mw-content-ltr and
-rtl. Add another rule to catch things outside the content area (which
should float based on the UI language).

Bug: T198774
Change-Id: I29b71a2e52139e540d719b61964084170d36bc5e