What makes Linux appealing to me is the extent of customizability, but I didn’t find many answers when looking up with desktop environment is them most customizable. Some say KDE is most customizable than say, Gnome, but doesn’t Gnome support CSS customization while KDE doesn’t?
No desktop environment. Get a compositor, a runner/menu/app-grid, maybe a panel or dock, set some shortcuts, done desktop environment. It’s how most of wayland outside KDE/Gnome currently works.