The system has constants for how scrollbars should be sized.  We should continue to obey those.

We've run into accessibility problems in the past with narrower scrollbars.  Edge's behavior here is something we should explicitly not copy.  If Microsoft thinks such scrollbars are how apps should behave in general, they can adjust the system-wide theme to do so by default.  This will allow people with accessibility needs to control that width across the system.