Calculadora Javascript

Question

What am I doing wrong with my code?
https://code.sololearn.com/WVE6ATE9Xj2A/?ref=app

Answer 1

The "resultado" variable is empty and you need to save each document.getElementById() in a variable or object to use the onclick method and access/change it values

Answer 2

Deleted all

Answer 3

Need some correction, you need to add overflow hidden in css result class