选择符结构树

.demo_box {background-color: #ff4e00;}

根据旁边的 HTML 结构输入一个选择符，查看结构变化，选中的节点是……

<div class="demo_box">
    <div class="a"></div>
    <div class="b">
      <div class="b1"></div>
    </div>
    <div class="c">
      <div class="c1">
        <div class="c1_1">
          <div class="c1_1_1"></div>
          <div class="c1_1_2"></div>
          <div class="c1_1_3"></div>
          <div class="c1_1_4"></div>
        </div>
      </div>
      <div class="c2"></div>
      <div class="c3">
        <div class="c3_1"></div>
      </div>
    </div>
    <div class="d">
      <div class="d1">
        <div class="d1_1"></div>
        <div class="d1_2"></div>
      </div>
    </div>
  </div>