Detailed explanation of the flexible use of CSS grid system in projects

<div id="app">
  <div class="grid-container">
    <div style="width: 25%; height: 220px; float: left; background-color: #FF6600; "></div>
    <div class="row" style="width: 75%; float: right;">
      <div class="col-3" v-for="(item, index) in groupListCol3" :key="index">
        <div class="groups-cell">{{item.name}}</div>
      </div>
    </div>
    <div class="row" style="width: 100%;">
      <div class="col-4" v-for="(item, index) in groupListCol4" :key="index">
        <div class="groups-cell">{{item.name}}</div>
      </div>
    </div>
  </div>
</div>

.grid-container {
      width: 100%;
    }
    .grid-container *{
      box-sizing: border-box;
    }

    .grid-container .row:before,
    .grid-container .row:after {
      content: "";
      display: table;
      clear: both;
    }

    .grid-container [class*='col-'] {
      float: left;
      min-height: 1px;
      /*-- gutter --*/
      padding: 0 0 20px 20px;
    }
    .grid-container .col-3{
      width: 33.33%;
      height: 120px;
    }
    .grid-container .groups-cell {
      background-color: #66d3ff;
      height: 100px;
    }
    .grid-container .col-4 {
      width: 25%;
      height: 120px;
    }
    .grid-container .col-4:nth-child(4n+1) {
      padding: 0 0px 20px 0px;
    }

<script src="https://cdn.bootcss.com/vue/2.5.16/vue.js"></script>
<script>
  new Vue({
    el: '#app',
    data: {
      groupListCol3: [],
      groupListCol4: []
    },
    created () {
      let list = [
        {name: 'A'},
        {name: 'B'},
        {name: 'C'},
        {name: 'D'},
        {name: 'E'},
        {name: 'F'},
        {name: 'G'},
        {name: 'H'},
        {name: 'I'},
        {name: 'J'},
        {name: 'K'},
        {name: 'L'}
      ]
      if (list.length > 6) {
        this.groupListCol3 = list.slice(0, 6)
        this.groupListCol4 = list.slice(6)
      } else {
        this.groupListCol3 = list
      }
    }
  })
</script>