I do mean scrolling with the touchpad, in my case edge scrolling, over the default GTK scrollbar. I haven't tried it with the overlay scrollbar.
The result of edge scrolling over the GTK scrollbar in evince is that the document smoothly scrolls, whereas edge scrolling a few pixels to the left over the document makes the document scroll in larger jumps.
I do mean scrolling with the touchpad, in my case edge scrolling, over the default GTK scrollbar. I haven't tried it with the overlay scrollbar.
The result of edge scrolling over the GTK scrollbar in evince is that the document smoothly scrolls, whereas edge scrolling a few pixels to the left over the document makes the document scroll in larger jumps.