My Commentary
Bam! Payday.
To paraphrase the official spec (source), "Dynamic Viewport-Percentage Units" like dvh
are
defined by the height of the viewport minus the browser UI, so
authors can make content exactly fit within the viewport --
whether browser doodads like address bars and toolbars are visible
or not.
I don't know why I didn't come across this solution first; it's
clearly the most logical one, but I'd never heard of it. Now you
have.