Where are the artifacts on the site from?

Question

css

Hello.
In chrome, this is what happens.
While it is difficult to reproduce. (when opening/closing a dropdown, and with a sharp hover)
Sometimes it's just a black background, sometimes random parts of the page fall into it.
Reproducible only in Chrome (71).

Answer 1

And so)
How simple everything was)
The link and the drop-down have a common parent, in the properties of which the drop-down has an animation with perspective. The link doesn't have anything like that. So this animation worked on it (which is not particularly logical) But the link property helped .perspective: 2000px;
backface-visibility: hidden;

Answer 2

delete with all the ends of the "lame" - it has become a virus ...