testing/web-platform/tests/css/css-will-change/will-change-abspos-cb-dynamic-001.html


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<!doctype html>
<meta charset="utf-8">
<title>CSS Test: will-change: position turns an element in an abspos containing block when changed dynamically.</title>
<link rel="author" title="Emilio Cobos Álvarez" href="mailto:emilio@crisal.io">
<link rel="author" title="Mozilla" href="https://mozilla.org">
<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1499863">
<link rel="help" href="https://drafts.csswg.org/css-will-change/#will-change">
<link rel="match" href="will-change-abspos-cb-001-ref.html">
<style>
  .container {
    border: 1px solid green;
    width: 100px;
    height: 100px;
    margin-top: 100px;
  }
  .abspos {
    position: absolute;
    top: 0;
    left: 0;
    background: orange;
    height: 20px;
    width: 20px;
  }
</style>
<div class="container">
  <div class="abspos"></div>
</div>
<script>
onload = function() {
  let container = document.querySelector(".container");
  container.offsetTop;
  container.style.willChange = "position";
}
</script>