Sometimes things you see in UI are not obviously scrollable. It’s your job as UI designer to help users understand there’s more than is immediately visible. Here’re some ways to do this:
1. (Leftmost) Bad, no indication
2. Scrollbar visible before you tried to scroll. Remember: user doesn’t know yet it can be scrolled!
3. Make sure last visible item is always cut in half. Can be programmed easily
4. Gradient indicating hidden parts
5. Explicit scroll button