Story 1628: Fix some of the mobile VE toolbar styles

This doesn't fix everything, but fixes the major glaring styling
problems. For the rest of it, we're going to wait until Trevor
implements skin support in the MW build of OO-ui.

Change-Id: I72f689d58133dad783ccf80e8e4758195f3bd28f
Merge "Story 1628: Fix some of the mobile VE toolbar styles"