<style>
.container {
  width: 100px;
  background-color: red;
}

.fill {
  height: -webkit-fill-available;
}

.overflow-sibling {
  width: 100px;
  height: 100px;
  background-color: green;
}
</style>
<!-- PASS if no red -->
<div class=container>
  <div class=fill></div>
  <div class=overflow-sibling></div>
</div>