<style>
  #x {
    container-type: inline-size;
    position: sticky;
    width: 10%;
  }
  :read-only {
    border-width: 250px;
  }
</style>
<script>
  if (window.testRunner)
    testRunner.dumpAsText();
  onload = () => {
    location.hash = 'x';
    document.designMode = 'on';
  };
</script>
<iframe id="x"></iframe>
This test passes if it doesn't crash.