由于官方API提供的显示模态弹窗，只能简单地显示文字内容，不能对对话框内容进行自定义，欠缺灵活性，所以自己从模态弹窗的原理角度来实现了自定义的模态对话框。

wx.showModal修改样式后的效果，如下图所示：

index.wxml代码：

<!--index.wxml-->
<button class="show-btn" bindtap="showDialogBtn">弹窗</button>
<!--弹窗-->
<view class="modal-mask" bindtap="hideModal" catchtouchmove="preventTouchMove" wx:if="{{showModal}}"></view>
<view class="modal-dialog" wx:if="{{showModal}}">
  <view class="modal-title">添加数量</view>
  <view class="modal-content">
    <view class="modal-input">
      <input placeholder-class="input-holder" type="number" maxlength="10" bindinput="inputChange" class="input" placeholder="请输入数量"></input>
    </view>
  </view>
  <view class="modal-footer">
    <view class="btn-cancel" bindtap="onCancel" data-status="cancel">取消</view>
    <view class="btn-confirm" bindtap="onConfirm" data-status="confirm">确定</view>
  </view>
</view>

index.wxss样式代码：

/**index.wxss**/
.show-btn {
  margin-top: 100rpx;
  color: #22cc22;
}
.modal-mask {
  width: 100%;
  height: 100%;
  position: fixed;
  top: 0;
  left: 0;
  background: #000;
  opacity: 0.5;
  overflow: hidden;
  z-index: 9000;
  color: #fff;
}
.modal-dialog {
  width: 540rpx;
  overflow: hidden;
  position: fixed;
  top: 50%;
  left: 0;
  z-index: 9999;
  background: #f9f9f9;
  margin: -180rpx 105rpx;
  border-radius: 36rpx;
}
.modal-title {
  padding-top: 50rpx;
  font-size: 36rpx;
  color: #030303;
  text-align: center;
}
.modal-content {
  padding: 50rpx 32rpx;
}
.modal-input {
  display: flex;
  background: #fff;
  border: 2rpx solid #ddd;
  border-radius: 4rpx;
  font-size: 28rpx;
}

.input {
  width: 100%;
  height: 82rpx;
  font-size: 28rpx;
  line-height: 28rpx;
  padding: 0 20rpx;
  box-sizing: border-box;
  color: #333;
}
input-holder {
  color: #666;
  font-size: 28rpx;
}

.modal-footer {
  display: flex;
  flex-direction: row;
  height: 86rpx;
  border-top: 1px solid #dedede;
  font-size: 34rpx;
  line-height: 86rpx;
}
.btn-cancel {
  width: 50%;
  color: #666;
  text-align: center;
  border-right: 1px solid #dedede;
}
.btn-confirm {
  width: 50%;
  color: #ec5300;
  text-align: center;
}

index.js代码如下：

/index.js

//获取应用实例

var app = getApp()
Page({
  data: {
    showModal: false,
  },
  onLoad: function () {
  },
  /**
   * 弹窗
   */
  showDialogBtn: function () {
    this.setData({
      showModal: true
    })
  },
  /**
   * 弹出框蒙层截断touchmove事件
   */
  preventTouchMove: function () {
  },
  /**
   * 隐藏模态对话框
   */
  hideModal: function () {
    this.setData({
      showModal: false
    });
  },
  /**
   * 对话框取消按钮点击事件
   */
  onCancel: function () {
    this.hideModal();
  },
  /**
   * 对话框确认按钮点击事件
   */
  onConfirm: function () {
    this.hideModal();
  }
})