<dl>
  <dt>1-1. flex布局左右</dt>
  <dd class="box-1-1">
    <div class="layout">
      <div class="left">分类列表区域</div>
      <div class="right">主要内容区域<p>这是p标签的内容</p></div>
    </div>
  </dd>
  <dt>1-2. flex布局右左</dt>
  <dd class="box-1-2">
    <div class="layout">
      <div class="left">分类列表区域</div>
      <div class="right">主要内容区域<p>这是p标签的内容</p></div>
    </div>
  </dd>
  <dt>1-2. flex布局右左通过flex中的order属性</dt>
  <dd class="box-1-3">
    <div class="layout">
      <div class="left">分类列表区域</div>
      <div class="right">主要内容区域<p>这是p标签的内容</p></div>
    </div>
  </dd>
</dl>

dl{
  padding: 0;
  margin: 10px;
  dt{
    margin-top: 10px;
    font-size: 20px;
    color: #fff;
    background-color: #00c;
    height: 50px;
    line-height: 50px;
    padding: 0 10px;
  }
  dd{
    border: 1px solid #ccc;
    margin: 0;
    height: 200px;
  }
  .layout{
    display: flex;
  }
  .left{background-color: pink; padding: 10px;}
  .right{background-color: skyblue; padding: 10px;}
}
.box-1-1{
  .left{
    width: 200px;
  }
  .right{
    flex-grow: 1;
  }
}
.box-1-2{
  .layout{
    flex-direction: row-reverse;
  }
  .left{
    width: 200px;
  }
  .right{
    flex-grow: 1;
  }
}
.box-1-3{
  .left{
    width: 200px;
    order: 1;
  }
  .right{
    flex-grow: 1;
  }
}