效果 

wxml

<!--新增（点击按钮）-->
<image class='img' src="{{add}}" bindtap='add_mode'></image>
<!-- 弹窗 -->
<view class="modal" wx:if="{{showModal}}">
  <view class="modal-content">
    <form bindsubmit="add_info">
      <view class="modal_title">上传文件</view>
      <view class="modal-buttons">
        <view class="one_btn" bindtap="submit">确认</view>
        <view class="two_btn" bindtap="cancel">取消</view>
      </view>
    </form>
  </view>
</view>

wxss

/* 窗口 */
.modal-content {
  background-color: white;
  width: 90%;
  height: 80%;
  border-radius: 8rpx;
  position: relative;
}

/* 模态框标题 */
.modal_title {
  padding: 3%;
  font-size: 110%;
  font-weight: bold;
}

/* 按钮 */
.modal-buttons {
  width: 100%;
  height:7%;
  display: flex;
  bottom: 0;
  position: absolute;
  font-weight:bold;
}
.one_btn{
  flex:1;
  display: flex;
  align-items: center;
  justify-content: center;
  background-color: #4b97e7;
  border-top: 1rpx solid #4b97e7;
  color: #fff;
  border-radius: 0;
}
.two_btn{
  flex:1;
  display: flex;
  align-items: center;
  justify-content: center;
  width: 100%;
  border-top: 1rpx solid #4b97e7;
  border-radius: 0px;
  background-color: #fff;
  color: #4b97e7;
}

js

const app = getApp()
Page({
  data: {
    add: app.globalData.icon + 'index/add.png',
    showModal: false // 控制模态框的显示和隐藏: false,
  },
  // 打开上传文件弹窗
  add_mode(){
    this.setData({
      showModal:true
    })
  },
  // 取消弹窗
  cancel(){
    this.setData({
      showModal:false
    })
  },
  //确认弹窗内容
  submit(){
    console.log('确认')
  }
})