css/css-overflow/nested-scroll-markers-under-content-visibility-auto-ref.html

<!doctype html>
<meta charset="utf-8">
<title>::scroll-markers with content-visibility: auto ancestors and subscrollers (ref)</title>
<link rel="help" href="https://drafts.csswg.org/css-overflow-5/#scroll-marker-pseudo">
<link rel="author" href="mailto:vmpstr@chromium.org">
<style>
  #scroller {
    width: 600px;
    height: 300px;
    overflow: scroll;
    scroll-marker-group: after;
  }

  .subscroller {
    scroll-marker-group: after;
    overflow: scroll;
    width: 600px;
    height: 100px;
  }

  .cv-placeholder {
    contain: strict;
    width: 100px;
    height: 100px;
  }

  #scroller::scroll-marker-group {
    border: 3px solid black;
    padding: 5px;
    height: 20px;
    display: block;
  }

  .item {
    height: 200px;
  }

  .item::scroll-marker {
    content: "";
    width: 10px;
    height: 10px;
    background-color: blue;
    border-radius: 50%;
    display: inline-block;
  }

  .spacer {
    height: 10000px;
  }
</style>
<div id="scroller">
  <div class=cv-placeholder>
    <div class=subscroller>
      <div class=item></div> <div class=item></div> <div class=item></div>
    </div>
  </div>
  <div class=item></div> <div class=item></div> <div class=item></div>
  <div class=spacer></div>
  <div class=cv-placeholder>
    <div class=subscroller>
      <div class=item></div> <div class=item></div> <div class=item></div>
    </div>
  </div>
</div>