Check the "Try it" box in this page https://developer.mozilla.org/en-US/docs/Web/CSS/backdrop-filter. Or open the problematic frame only https://interactive-examples.mdn.mozilla.net/pages/css/backdrop-filter.html Result: Wrong layout and the example itself is not shown. When inspecting the example container, nothing is highlighted.
<rdar://problem/100727661>
This is not related to grid layout. What happens is that WebKit doesn't support backdrop-filter, so MDN doesn't show the live example, since it wouldn't work at all. *** This bug has been marked as a duplicate of bug 224899 ***