Playground de select en HTML

<label for="baseline-select">Elige una tecnología</label>
<select id="baseline-select" name="baseline-choice">
  <option value="option-1" selected>Selecciona una opción</option>
  <hr />
  <optgroup label="Frontend">
    <option value="html">HTML</option>
    <option value="css">CSS</option>
    <option value="javascript">JavaScript</option>
  </optgroup>
  <optgroup label="Plataforma web">
    <option value="web-components">Web Components</option>
    <option value="forms">Forms</option>
  </optgroup>
</select>