UNI-APP_iphone bottom safe area

The item needs to make a fixed button at the bottom (above the tabbar), and the style is no problem under normal mobile phones.Under iPhone xr and iphone11, the location is incorrect. The problem is that the iphone has an additional safe area problem

Probably this one.It is also included in the height of the entire page. If this height is not added, the fixed positioning position will be lower than the original one (so, the project still needs to be tested on the real machine to be accurate, and the simulator cannot be measured accurately).
Solution: https://ask.dcloud.net.cn/article/36494

padding-bottom: constant(safe-area-inset-bottom);padding-bottom: env(safe-area-inset-bottom);

Explain a description: var(–safe-area-inset-bottom) The height of the safe area, directly with the unit (px), only the mobile phone with the safe area has this value, the others are 0
ps:var(--safe-area-inset-bottom) This attribute only works in js and html styles.** (I have tried it briefly, and how to write it can be used in js and html styles.This is unknown, if anyone knows, please leave a message, thank you!) **
If you want to fix the positioning at the bottom

.bottom{bottom: env(safe-area-inset-bottom);}/*If you want to be above the tabbar, add the height of the tabbar, for example, the height of the tabbar is 120rpx*/.bottom{bottom: calc(120rpx + env(safe-area-inset-bottom));}