1.iphoneX的尺寸 375*812 上边有44px的危险区，下边有34px的危险区，剩下的是安全区。
2.viewport设值cover
1 <meta name="viewport" content="width=device-width,initial-scale=1.0, minimum-scale=1.0, maximum-scale=1.0, user-scalable=no,viewport-fit=cover">
3.媒体查询适配样式
1 @media only screen and (device- 375px) and (device-height: 812px) and (-webkit-device-pixel-ratio: 3) { 2 3 }