 width: 600px;
    height: 270px;
  }

  #scroller::scroll-marker-group {
    height: 20px;
    width: 200px;
  }

  #scroller div::scroll-marker {
    content: "Marker";
    width: 100px;
    height: 20px;
    display: inline-block;
  }

  #scroller::scroll-button(left) {
    content: "<";
  }
</style>
<div id="scroller">
  <div></div>
  <div></div>
</div>
<script>
  async function run() {
    const kTab = '\uE004';
    await new test_driver.Actions()
      .keyDown(kTab)
      .keyUp(kTab)
      .send();
