Portrait / landscape layout recalculation
On my iPad Pro / Safari, the UI would be much more usable if the app could optionally recalculate a different layout when the display is rotated between portrait and landscape modes, as currently a lot of screen real estate isn't getting used and I would really like to see more lines.
I wonder if the relevant new advanced CSS media queries would help here ? (Don't know how much is supported in Safari iOS yet.)

DiffNow already responds to screen resizing (it uses CSS media queries). It cannot dynamically change splitter orientation if that’s what you mean since this is done on the server, before the iframe is generated.