css/css-overflow/scrollbar-gutter-dynamic-001.html

<!doctype html>
<meta charset="utf-8">
<title>CSS Overflow: scrollbar-gutter changing dynamically</title>
<link rel="help" href="https://drafts.csswg.org/css-overflow-4/#scrollbar-gutter-property">
<link rel="stylesheet" href="/fonts/ahem.css">
<link rel="match" href="scrollbar-gutter-dynamic-001-ref.html">

<style>
  #scroller {
    font: 100px/1 Ahem;
    color: green;
    overflow-y: auto;
    width: 300px;
    height: 300px;
  }
</style>
<div id="scroller">X X</div>
<script>
  scroller.offsetTop;
  scroller.style.scrollbarGutter = "stable";
</script>