css/css-overflow/column-scroll-marker-dynamic-style-update.html

<!DOCTYPE html>
<title>CSS Overflow Test: ::scroll-marker dynamic style change</title>
<link rel="help" href="https://drafts.csswg.org/css-overflow-5/#scroll-buttons">
<link rel="match" href="../reference/ref-filled-green-100px-square.xht">
<style>
#scroller {
  overflow: hidden;
  scroll-marker-group: before;
  columns: 1;
  gap: 0;
  height: 100px;
  width: 100px;
}
  #scroller::scroll-marker-group {
    display: flex;
    width: 100px;
    height: 100px;
    background: red;
  }
  #scroller::column::scroll-marker {
    width: 20px;
    height: 100px;
    content: "";
  }
  #scroller.extra::column::scroll-marker {
    display: flex;
    background: green;
  }
</style>
<p>Test passes if there is a filled green square and <strong>no red</strong>.</p>
<div id="scroller">
  <div style="height:401px;"></div>
</div>
<script>
  document.body.offsetTop;
  scroller.className = "extra";
</script>