You can now use CSS Grid to fix this.
<div class="outer">
<div class="top"> </div>
<div class="below"> </div>
</div>
And the css for this:
.outer {
display: grid;
grid-template: 1fr / 1fr;
place-items: center;
}
.outer > * {
grid-column: 1 / 1;
grid-row: 1 / 1;
}
.outer .below {
z-index: 2;
}
.outer .top {
z-index: 1;
}