<dl>
  <dt>1-1. grid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. grid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>
</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: grid;
}
.left{background-color: pink; padding: 10px;}
.right{background-color: skyblue; padding: 10px;}

.box-1-1 .layout{
  grid-template-columns: 300px 1fr;
}
.box-1-2 .layout{
    grid-template-columns: 1fr 200px;
}
.box-1-2 .left{
  grid-area: 1 / 2 / 2 / 3;
}