css/css-flexbox/overflow-auto-001.html

<!DOCTYPE html>

<title>Tests that we consider main axis sizes to be definite in column flexboxes
when the height is an explicit definite height, even if the container does
not have a definite main axis size.</title>
<link rel="author" title="Google LLC" href="https://www.google.com/">
<link rel="help" href="https://drafts.csswg.org/css-flexbox/#algo-main-item">
<link rel="match" href="../reference/ref-filled-green-100px-square.xht">

<style>
/* Make it possible for red to appear in webkit/blink browsers. But the test
 * still works in other browsers, you'll just get a grey scrollbar that
 * shouldn't be there.
 */
::-webkit-scrollbar-track, ::-webkit-scrollbar-thumb, ::-webkit-scrollbar {
  width: 10px;
  background: red;
}

#flex {
  display: flex;
}

#item {
  height: 300px;
  overflow: auto;
  scrollbar-color: red;
}

#child {
  height: 600px;
}
</style>

<p>Test passes if there is a filled green square and <strong>no red</strong>.</p>

<div style="width: 100px; height: 100px; background: green;"></div>

<div id="flex">
  <div id="item">
    <div id="child">
      Text
    </div>
  </div>
</div>

<script>
var item = document.getElementById('item');
item.offsetHeight;
item.style.width = 0;
</script>