The easiest way to do this is to make the text a child of the div
with the background image. The change to min-size is so that if
the text wraps often enough on narrow screens, the header expands
vertically rather than the text spilling over.
Fixes#3259
This fixes a glitch highlighted in #3259, where the css class stopped applying
when the view was moved to a different controller.
We're moving to having each view responsible for their layout, and commonly having
override classes explicitly in the relevant views. So we can follow that pattern here.
