chromium/third_party/blink/web_tests/external/wpt/css/css-position/position-relative-table-thead-top-absolute-child.html

<!DOCTYPE html>
<title>position:relative top constraint should behave correctly for &lt;thead&gt; elements</title>
<link rel="match" href="position-relative-table-top-ref.html" />
<link rel="help" href="https://www.w3.org/TR/css-position-3/#rel-pos" />
<meta name="assert" content="This test checks that the position:relative top constraint behaves correctly for &lt;thead&gt; elements" />

<style>
table {
  border-collapse:collapse;
}

td {
  padding: 0;
}

td > div {
  height: 50px;
  width: 50px;
}

.group {
  display: inline-block;
  position: relative;
  width: 150px;
  height: 200px;
}

.indicator {
  position: absolute;
  background-color: red;
  left: 0;
  top: 100px;
  height: 50px;
  width: 50px;
}

.relative {
  position: relative;
  top: 50px;
  background-color: green;
}

.absolute {
  position: absolute;
  top: 50px;
  background-color: green;
}
</style>

<div class="group">
  <div>
    <div class="indicator"></div>
    <table>
      <thead class="relative">
        <tr><td><div class="absolute"></div></td></tr>
      </thead>
      <tbody>
        <tr><td><div></div></td></tr>
      </tbody>
    </table>
  </div>
</div>

<div>You should see a green box above. No red should be visible.</div>