OOjs UI: Fix z-index and font size for default overlay

Authored by matmarex on Fri, Jan 12, 9:52 PM.

Description

OOjs UI: Fix z-index and font size for default overlay

OOUI dropdown menus should appear on top of the fixed header
and their font size should match the body text.

For example, on Special:MovePage:

Bug: T183069
Change-Id: I291d852f49507e58082ac95e59cb115170aa809a

Details