vue如何实现点击按钮切换背景颜色的效果

<div class="btnTitle">  <div class="btn-bg" :class="{bg:time == 3}" @click="changeBg(3)">15天</div>  <div class="btn-bg" :class="{bg:time == 4}" @click="changeBg(4)">30天</div> </div> <div class="btnTitle">  <div class="btn-bg" :class="{bg:increase == 5}" @click="changeBg(5)">增量</div>  <div class="btn-bg" :class="{bg:increase == 6}" @click="changeBg(6)">总量</div> </div> // 在methods方法里面 data () { time: 3,  increase: 5,  }, methods: { changeBg (index) {  if (index === 3 || index === 4) {  this.time = index  } else if (index === 5 || index === 6) {  this.increase = index  } else {  this.sort = index  } } } // css样式 <style lang="scss">.bg {  background-color: rgb(12, 197, 89);  color: #fff;  }  .btnTitle {    display: flex;    width: 400px;    border: 1px solid #ccc;    background-color: #fff;    margin-left: 10px;    border-radius: 5px;    .btn-bg {     width: 50%;     height: 40px;     text-align: center;     line-height: 40px;     border-radius: 5px;    }   } </style>