<style>
.flex-container { 
  display: flex; 
  flex-direction: column; 
}

.fixed-flex-item {
  position: fixed;
  height: 200px;
}
.heigh-percentage-descendant {
  height: 100%;
}

.sibling {
  height: 100%; 
}

</style>
PASS if no crash or assert.
<div class=flex-container>
  <div class=fixed-flex-item>
    <div class=heigh-percentage-descendant></div>
  </div>
  <div class=sibling></div>
</div>
<script>
if (window.testRunner)
  testRunner.dumpAsText();
</script>