 {
    margin: 0;
  }

  :root {
    scroll-marker-group: before;
  }

  :root::scroll-marker-group {
    border: 3px solid black;
    padding: 5px;
    height: 20px;
    display: block;
    position: fixed;
    top: 0;
  }

  div {
    width: 600px;
    height: 300px;
    margin-bottom: 20px;
    background: blue;
  }

  div:first-of-type {
    margin-top: 40px;
  }

  div::scroll-marker {
    content: "";
    width: 20px;
    height: 20px;
    background-color: red;
    display: inline-block;
    margin-r