Make scroll bars homogenous (if possible) across platforms

[bakkdoor]

Right now scroll bars look differently on each platform. If we can, we should:

• Make them look and feel the same
  or alternatively:
• Make them work in a way that the remaining UI elements don't bump around whenever scrollbars transition from being shown or hidden (this e.g. happens on a mac whenever you don't have a mouse connected and start/stop using the trackpad and whenever new content is being added and rendered that causes scrollbars to appear).