vue-element-admin 跨屏兼容问题

在手机和ipad上弹窗有一点小问题
<img width="844" alt="vue-admin-1" src="https://user-images.githubusercontent.com/45477743/53929649-6cd4cb80-40c9-11e9-8a07-9e93294c172f.png">
<img width="510" alt="vue-admin-2" src="https://user-images.githubusercontent.com/45477743/53929666-7bbb7e00-40c9-11e9-820f-765ee2be9d14.png">
