Huh. That’s odd. It must be something to do with my browser. The scroll bar shows in a fresh firefox profile, but not in falkon. In falkon, I can still use shift+scroll wheel to scroll horizontally, and the bar even goes from pink to red when I hover over it, but if refuses to be dragged!
The css Itch uses is a bit weird. If you test around, also try changing size of the page. Elements on the page are sensitive to the page width and such things. Some even disappear entirely, if your page is not wide enough.
Ohhhh. Why did I not know that you can shift-mousewheel for horizontal scroll...