Full page demo content-shrink on mobile

The full page demo will suddenly shrink the content (change zoom level maybe?) on mobile safari when scrolling down. I suspect it happens when _3d - Holograms_ gets loaded but isn't yet in the viewport because the video width is wider than the rest. It's not necessarily a bad thing but is unexpected and jarring.


**Test case:** https://infinite-scroll.com/demo/full-page/

Start with the full-page demo at https://infinite-scroll.com/demo/full-page/ and reproduce the content-width change while scrolling in mobile Safari. Check whether loading the _3d - Holograms_ section triggers the shrink; done means the demo no longer unexpectedly changes zoom or content width during that interaction.

Written by the indexing model from the issue text.