[feature request] add scrollbar customization to appearance settings / themes customization

[dnfoo]

It seems there is quite a heated debate on scrollbars and their arrows going on, resulting in lots of people (including me) wanting to use a theme they like but having their workflow broken by the scrollbar settings of that theme (and, as in my case all preinstalled themes for linux mint).
While constructing a solution that works for me I found that forums are full of people spending lots of time trying to change their scrollbars and fiddling with system internals and app settings they don't really understand.

It seems to me that themes customization would be the perfect place to change scrollbar settings, so users can set them easily and system-wide the way that works for them.