TIL: CSS trick to move a child behind it's parent. Did not need it in the end and used a clip-path instead.

.parent {
transform-style: preserve-3d;
}

.child {
transform: translateZ(-1px)
}

@michaelvaes that might well be the fix I needed to remove a hack in my personal site, thanks!
@akamatchstic I had a popperjs tooltip where I wanted the arrow to be in a different arrow-color. Their default setup does not allow for that.