There seems to be lots of changes to the layer tree, causing allocations and repainting. Probably affects desktop too, but it is incredibly noticeable on android. I will investigate further.
Problem number one: there is a scrollframe which scrolls a tiny amount nested within the main scrollframe. The inner scrollframe captures lots of swipes, which makes scrolling feel janky. This affects android, and desktop if you make the window narrow. It is because the body element has `overscroll-x: hidden` set on it, which according to https://stackoverflow.com/a/6433475 implies `overscroll-y: auto`. So we end up with scrollbars on the body as well as the viewport. I doubt this was the desired result, but maybe it is the correct one. Tim, do you know about this? Do you think there is anything we can do here?
Chrome doesn't get a second scrollable like we do. Do you know why? Do all the problems go away if we don't get the second scrollable?
Chrome does get the second scrollable for me. No, there are other problems too: it layerizes very poorly when items move about. If the body was tall enough to contain its content it wouldn't get a scrollbar, even with "overscroll-y: auto", right? It seems like it is only just shorter than its content, therefore we get a scrollbar which only moves a tiny amount. I can't see why it isn't the correct height.