cleanup some `pre` css inheritance

We had various overrides of the bootstrap defaults for font-size and line-height every time we made a pre tag,
and then some overrides of our overrides when we wanted something slightly different.

This moves the most basic overrides to apply to all pre tags,
reducing the number of downstream changes we need.
Merge pull request #5534 from minrk/pre-css

cleanup some `pre` css inheritance