Well, to start, line 64 needs to be this.items.push, otherwise it fails to load. But once I do that, I think I can see what you’re talking about. The other elements shift slightly. It’s hard to catch, but once you see it, it’s painfully obvious - everything is shifting because the scroll bar goes away. I made the issue go away with this:
body {
height: 1000px;
}
Obviously, you don’t need to keep it at 1000px, but you could also hide the scroll bar. I hope this helps, but I might not be seeing the same issue you are (I’m using latest Safari).