[walderf]

not 100% sure if this will help, but i use this to disable shadows and weird border-glow-edge related stuff on "my theme". yes, i know you didn't want CSS hacks, but... https://github.com/walderf/dotfiles/blob/main/.config/gtk-3....

here's what "my theme" looks like with this in place - https://i.imgur.com/SZ1iZjf.png

if you're curious, here's the rest of it - https://github.com/walderf/dotfiles/tree/main/.local/share/t...

it's not perfect, but, it's alright, really. maybe i will finish it and package it better some year. doubt it, though! :)