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<ol class="my-custom-list-style">
  <li>1</li>
  <li>2</li>
  <li>3</li>
</ol>

ol.my-custom-list-style {
  list-style-type: my-custom-list-style-type;
}

@counter-style my-custom-list-style-type {
  prefix: "(";
  suffix: ")";
  system: extends trad-chinese-informal;
}