Some times the buttons cannot tap and another issue.

[caichunjian520]

1. The button gesture modifier is attached to Text which may cause issue that user fail to touch button. Try to move the .gesture modifier to ZStack seems to solve the issue.
2. If user taps one of add, minus, multiply, divide buttons, then taps clear button cannot dismiss highlight color of those buttons. In iOS calculator, when first tap clear button will set Display Area to 0, and second tap will dismiss highlight color.