Removed redundant CSS rules in Minerva. They were duplicated from core.
Bug: T325574
Depends-On: I66682ea78c796bd587e3fa002b4176cbdd1ccd0d
Change-Id: I89d66406cea65ff94819ac70c0ee54a7aa6bf6ba
Added a stylesheet for when a user views Special:Preferences in mobile
Bug: T311717
Depends-On: Ia7a730cd7f009dbb921a810f27fae4a9ee66f793
Change-Id: I83558ca5de50fa7d8c7d75572ffa1c600f660d66