<div class="div3">             <ul>                 <li>123123123123123123123</li>                 <li>                     <ul>                         <li>1231231231231231</li>                     </ul>                 </li>             </ul>         </div>就像這個例子，我給他設置樣式如下兩種方式，結果都一樣.div3 ul li{                background-color: red;             }             .div3 ul>li{                background-color: red;             }