chromium/chrome/browser/resources/chromeos/healthd_internals/line_chart/scrollbar.html

<style include="healthd-internals-shared">
  #outerDiv {
    overflow-x: scroll;
    overflow-y: hidden;
  }

  #innerDiv {
    height: 2px;
  }

  /* Avoid hiding scrollbar */
  #outerDiv::-webkit-scrollbar {
    -webkit-appearance: none;
  }

  #outerDiv::-webkit-scrollbar-thumb {
    background-color: var(--cros-ref-neutral70);
  }
</style>
<div id="outerDiv" class="horizontal-scrollbar-outer">
  <div id="innerDiv" class="horizontal-scrollbar-inner"></div>
</div>