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chromium/third_party/blink/web_tests/fast/forms/select-popup/popup-menu-appearance-custom-scrollbar-track-display-none.html 

<!DOCTYPE html>
<meta name=fuzzy content="maxDifference=0-3; totalPixels=0-100">
<script src="../../../resources/testdriver.js"></script>
<script src="../../../resources/testdriver-vendor.js"></script>
<script src="../../resources/ahem.js"></script>
<script src="../resources/picker-common.js"></script>

<style>
  select:focus {
    outline-width: 0;
  }
  select {
    width: 200px;
    font: 10px Ahem;
    appearance: none;
    background-color: white;
  }
  select::-webkit-scrollbar {
    width: 15px;
  }

  select::-webkit-scrollbar-track {
    background: orange;
    display: none;
  }
  select::-webkit-scrollbar-thumb {
    background: gray;
  }
</style>

<select>
  <option>This is an option</option>
  <option>This is an option</option>
  <option>This is an option</option>
  <option>This is an option</option>
  <option>This is an option</option>
  <option>This is an option</option>
  <option>This is an option</option>
  <option>This is an option</option>
  <option>This is an option</option>
  <option>This is an option</option>
  <option>This is an option</option>
  <option>This is an option</option>
  <option>This is an option</option>
  <option>This is an option</option>
  <option>This is an option</option>
  <option>This is an option</option>
  <option>This is an option</option>
  <option>This is an option</option>
  <option>This is an option</option>
  <option>This is an option</option>
  <option>This is an option</option>
  <option>This is an option</option>
  <option>This is an option</option>
  <option>This is an option</option >
</select>

<script>
  window.onload = openPickerAppearanceOnly(document.querySelector('select'));
</script>