This fixes a handful of issues that have come up with the form styling

in the administration UI:


The old deprecated textarea definitions were badly copy/pasted, and

   most were set to the textarea font-size value, which broke a few

   things.


Checkbox labels would move below the checkbox input if the label

   needed to wrap.


Description areas for fieldsets had some pretty rough spacing.


Input areas for fields didn't have access to the entire width of the

   form, causing some inputs to be too small when set to width: 100%.

Tested all the current forms in desktop and mobile modes, and at different

viewport widths, making sure they looked correct.
Tested a few places that used legacy textarea definitions, and saw that

they had the correct font and presentation.