Before the default style looked quite oxygenish. Now that we have settled on a style with Kirigami.ListSectionHeader component we can use the same style here to improve consistency between QWidget and QML lists that are displayed next to each other.
Global Shortcuts KCM (without scrollbar)
KRunner KCM (with scrollbar)
Global Shortcuts KCM
Frankly I would really like a vertical line separating the scrollbar from the content for just this reason. IIRC Breeze used to have that but it lost it for some reason. When the scrollbar isn't an overlay, we should try to make it look like one IMO.
Looking at lxr other users include (not exhaustive, I may have missed some)
Kexi (don't have it installed),
KPluginSelector (example where it is used?),
and public transport (optionally).
LGTM except for the abrupt end on the right side where the scrollbar's area begins, but this is a pre-existing problem with all things that butt up against a scrollbar in a scrollview, and I think we should add a vertical separator line to fix it universally.