HTML optgroup kullanımı

<!DOCTYPE html>
<html>

  <head>
    <title>optgroup Kullanımı</title>
  </head>

  <body>
    <select>
      <optgroup disabled label="İsviçre Arabaları">
        <option value="volvo">Volvo</option>
        <option value="saab">Saab</option>
      </optgroup>
      <optgroup label="Alman Arabaları">
        <option value="mercedes">Mercedes</option>
        <option value="audi">Audi</option>
      </optgroup>
    </select>
  </body>

</html>