Too many custom scrollbar projects (including this one) make the mistake of overriding everything helpful the browser does for you and then imperfectly reimplementing it.

The best technical approach is to make the scrollable element naturally scrollable with overflow: auto, and then put it inside a viewport element (overflow: hidden) narrow enough to cut off the scrollbar (there are plugins that can help you figure out exactly how wide the host's OS's scrollbars are).

Then, you're free to listen for scroll events and overlay your own custom scroller UI.