I prefer a dark theme with some high contrast elements. I came from AutoCad so very used to the black background. I also prefer few toolbars and lots of working space. Hotkeys over toolbars for sure.
I typically choose dark theme on any software if it’s an option. White or light colored backgrounds hurt my eyes after many hours of screen time.
Well, I use the Rhino UI “as is” except some floating toolbars in workspace like section and paneling tools, auxpecker, 3DE math, boltgen.
I tried customization several times but I always reverted the UI back.
The custom toolbar is sweet!
Same as others, I used to customize my toolbars in previous versions but gave up over the years.
But this sidebar idea in combination with the nearer command console is worth a try.