父元素flex:1 子元素height:100%

    <style>
        .box{
            display: flex;
            flex-direction: column;
            overflow: hidden;  //只要不是auto
        }
        .parent{
            flex: 1;
            min-height: 0;  //or height:0
        }
        .children{
            height: 100%;  //可正常继承
        }
    </style>
    <div class="box">
      <div></div>
      <div class="parent">
          <div class="children">
          </div>
      </div>
    </div>