uni-popup uni-mask 为什么总会有44px的高度

<uni-popup :show="confirmBuy" position="middle" type="middle" mode="fixed" v-on:hidePopup="closeConfirmBuy">
<view class="uni-popup-concent">
<view class="title">购买须知</view>
<view class='alert-light'>请认真阅读商品使用规则，非券码质量问题不接受纠纷</view>
<view class='alert-text alter-check' @tap='checkRead'>
<image :src="/static/images/buy/check${ifReadCheck ? '-on' : ''}.png"></image>
<text class='orange'>我已阅读并知晓【购买须知】和商品【使用规则】</text>
</view>
<view class='alert-text alter-check' @tap='checkConfirm'>
<image :src="/static/images/buy/check${ifRead ? '-on' : ''}.png"></image>
<view>我已阅读、理解并接受<text class='blue' @tap.stop='toProtocol'>【购买服务协议】</text></view>
</view>
<view class='btns'>
<button class='cancel' @tap='closeConfirmBuy'>取消</button>
<button class='confirm' @tap='clickConfirmBuy'>确认</button>
</view>
</view>
</uni-popup>