塊級元素右對齊/左對齊

html部分

<div class="father">
     <div class="son"></div>
</div>

css部分

 .father {
    width: 300px;
    background: green;
  }

  .son {
    width: 200px;
    height: 200px;
    margin-right: auto;   //左對齊
    background: red;
  }

 .father {
    width: 300px;
    background: green;
  }

  .son {
    width: 200px;
    height: 200px;
    margin-left: auto;   ///右對齊
    background: red;
  }