The best I've seen so far yet far from perfect when you try to actually do it. Just look how ugly do the window menus hot keys underlines look even on the screenshot. And that's not the only quirk even there, and there will be more on your actual machine.

There also is (or, perhaps, was? I haven't cheecked for a year) a problem with GTK3 apps which don't get skinned this way even if they use uncustomized window decorations.

In fact it fascinates me how hard it appears to restyle your widows to look like whatever you want.