My experience when working on large projects for "late adopter" users, i.e. people with very little experience with internet: When presented with heavily styled or non-standard versions of native elements (like form fields or scrollbars) they often ignored them or weren't able to use them.
So my advice is, don't style them unless really necessary. And if you do, don't overdo it.
If you plan to style the scrollbars for aesthetic reasons, don't even bother doing that. User's don't really care about how the native elements look, they are used to them. Also, most users these days won't even see the scrollbars - in most browsers, and especially on mobile platforms, scrollbars are hidden and will only appear when actively used.