I've also made my own scrollbar for a project, so I have enhanced super vision to see the edge cases: 1) scrollbar disappears on drag when the mouse moves out

I've also made my own scrollbar for a project, so I have enhanced super vision to see the edge cases: 1) scrollbar disappears on drag when the mouse moves out of the container. To fix you need to have a flag when the scrollbar is dragging and not call fadeout when true. 2) convenient UI feature: scrollbar can appear on hover, then disappear if user hasn't moved mouse, and reappear on mousemove. This is done in Facebook for example. This is accomplished by setting and clearing timeouts. (also, the bot left container for the scrollbar doesn't have a rounded corner) otherwise great job!