The pain point of mobile layout is: compatible with mobile devices of various resolutions, which are also mobile phones, and the resolution range of iPhone4-iPhoneX is already very wide; if you use px for layout, there will obviously be problems;
In the common pixel units px, em, and rem, em is the unit relative to the font-size of the parent element. I personally think that in use, em will be confusing; rem is relative to the root element and HTML, which is convenient for layout according to screen resolution. ;
The current mobile layout method: "horizontal percentage + vertical rem", while using flex layout;
https://www.cnblogs.com/ysshuai/p/6694339.html