I wanted to do a mockup of a UI a few moth back. It was moderately complex, I suppose. And I was just trying to find something that would let me build out a shell. I started on Linux and I found most of the UI frameworks to be quite disappointed and a bit involved for what I was wanting to do. I think I was splaying with Glade and then QT creator and realizing just how much boilerplate code I'd have to write to get things to look how I wanted.

I then ran over to Windows, because I recall having done similar things with WPF. I instantly recalled why I hated it though, as doing any custom styling on components is a miserable mess of boilerplate XML and overriding values I have little knowledge of and seem not related or tangentially related to what I was styling.

I was able to create what I wanted relatively easily with a mix of HTML and CSS though. I think something like WPF but with CSS-like styling would be nice.