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

<!DOCTYPE html>
<title>CSS Overflow Test: ::column::scroll-marker counters</title>
<link rel="match" href="column-scroll-marker-counters-ref.html">
<link rel="help" href="https://www.w3.org/TR/css-multicol-2/#column-pseudo">
<style>
  #scroller {
    overflow: hidden;
    scroll-marker-group: after;
    counter-reset: item;
    columns: 1;
    gap: 0;
    height: 100px;
    width: 100px;
  }
  #scroller::scroll-marker-group {
    border: 3px solid black;
    display: flex;
    height: 100px;
    width: 300px;
  }
  #scroller::column::scroll-marker {
    content: counter(item);
    counter-increment: item;
    background-color: green;
    border-radius: 50%;
    height: 100px;
    width: 100px;
  }
  .item {
    height: 100px;
    width: 100px;
  }
</style>
<div id="scroller">
  <div class="item">1</div>
  <div class="item">2</div>
  <div class="item">3</div>
</div>