You can dictate GTK and Qt's design. Also, I think for Chrome at least, it draws scrollbars using its own widget library — built on top of Skia, I think? Not s

You can dictate GTK and Qt's design. Also, I think for Chrome at least, it draws scrollbars using its own widget library — built on top of Skia, I think? Not sure what the widget-library part itself is called. You could definitely contribute to that.