<!DOCTYPE html>
<link rel="help" href="https://www.w3.org/TR/css-flexbox-1/#valdef-flex-direction-column-reverse">
<link rel="help" href="https://drafts.csswg.org/css-align/#gap-shorthand">
<style>
  .flexbox {
    display: flex;
    flex-direction: column-reverse;
    gap: 5px;
    position: relative;
    background-color: blue;
  }
  .flexbox > * {
    height: 10px;
    background-color: green;
  }
</style>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/resources/check-layout-th.js"></script>
<body onload="checkLayout('.flexbox')">
<div id=log></div>
<div class="flexbox" data-expected-height="40">
  <div data-offset-y="30"></div>
  <div data-offset-y="15"></div>
  <div data-offset-y="0"></div>
</div>
</body>
