W3School TIY
编辑您的代码：
<html> <body> <select> <optgroup label="Swedish Cars"> <option value="volvo">Volvo</option> <option value="saab">Saab</option> </optgroup> <optgroup label="German Cars"> <option value="mercedes">Mercedes</option> <option value="audi">Audi</option> </optgroup> </select> </body> </html>
查看结果: