<view class="body">
  <view class="nav bc_white">
    <view class="{{selected?‘red‘:‘default‘}}" bindtap="selected">系统提醒</view>
    <view class="{{selected1?‘red‘:‘default‘}}" bindtap="selected1">优惠活动</view>
    <view class="{{selected2?‘red‘:‘default‘}}" bindtap="selected2">123</view>
  </view>
  <view class="{{selected?‘show‘:‘hidden‘}}">for system</view>
  <view class="{{selected1?‘show‘:‘hidden‘}}">for activity</view>
  <view class="{{selected2?‘show‘:‘hidden‘}}">for activsadity</view>
</view>

page {
  background-color: rgb(243,243,243);
}

.nav {
  width: 100%;
  height: 80rpx;
  display: flex;
  flex-direction: row;
  background: #fff;
  justify-content: space-around;
}

.nav view {
  width: 180rpx;
  text-align: center;
}

.default {
  line-height: 80rpx;
  text-align: center;
  color: #000;
  font-weight: bold;
  font-size: 30rpx;
}

.red {
  line-height: 80rpx;
  text-align: center;
  color: rgb(0, 192, 10);
  font-weight: bold;
  font-size: 30rpx;
  border-bottom: 4rpx solid rgb(0, 192, 10);
}

.show {
  display: block;
  text-align: center;
}

.hidden {
  display: none;
  text-align: center;
}

 data: {
    selected: true,
    selected1: false
  },
  selected: function (e) {
    this.setData({
      selected1: false,
      selected2: false,
      selected: true
    })
  },
  selected1: function (e) {
    this.setData({
      selected: false,
      selected2: false,
      selected1: true
    })
  },
  selected2: function (e) {
    this.setData({
      selected: false,
      selected2: true,
      selected1: false
    })
  },