The white doesn't bother me, but the lack of differentiation between inactive window and active window title bars does.The most jarring thing so far is this fucking white title bar color. Why in the hell would you make that the default, and then worse, something that you can't change?
Edit: Found the workaround for it. That's a giant pain in the ass for something that shouldn't be the default to begin with.
BTW, Edge has a Dark Theme, which makes it look almost exactly like Steam.