Redo VE toolbar styling

Authored by Esanders.


Redo VE toolbar styling

A lot of CSS has been moved upstream since this was first written.

It is also possible to simplify the resizing of the toolbar by just
changing the base font size as all sizing in VE is done with ems.

MF's overriding of box-sizing necessitates another override.

Bug: T85025
Change-Id: Ifa646fe392b86ab5c9f4aa03cc3df833e49eab7e