<!DOCTYPE html>
<link rel="help" href="https://crbug.com/1129563">
<body style="contain: size layout;">
  <div id="target" style="contain: size layout;"></div>
  <div id="child"></div>
</body>
<script>
document.body.offsetTop;
const target = document.getElementById('target');
const child = document.getElementById('child');
target.appendChild(child);
</script>