css/css-overflow/column-scroll-marker-011.html

<!DOCTYPE html>
<html class="reftest-wait">
<title>multicol ::column::scroll-marker, add more columns</title>
<link rel="author" title="Morten Stenshorne" href="mailto:mstensho@chromium.org">
<link rel="help" href="https://drafts.csswg.org/css-overflow-5/#scroll-marker-group-pseudo">
<link rel="match" href="../reference/ref-filled-green-100px-square.xht">
<p>Test passes if there is a filled green square and <strong>no red</strong>.</p>
<style>
  #container {
    overflow: hidden;
    columns: 3;
    column-fill: auto;
    gap: 0;
    height: 100px;
    scroll-marker-group: before;
  }
  #container::scroll-marker-group {
    overflow: auto;
    display: flex;
    width: 100px;
    height: 100px;
    background: red;
  }
  #container::column::scroll-marker {
    width: 25px;
    height: 100px;
    flex: none;
    content: "";
    background: green;
  }
</style>
<div id="container">
  <div style="height:100px;"></div>
</div>
<script>
  requestAnimationFrame(()=> {
    requestAnimationFrame(()=> {
      document.documentElement.classList.remove("reftest-wait");
      container.style.height = "25px";
    });
  });
</script>