How are you approaching the problem?
This is a really good article on how to make one. Take a note from it and try styling it on your own.
Does the final result have to include a 2 output display like in the sample codepen? Do we also have to implement a max digits limit when the user enters too many numbers(also implemented in the sample codepen)? Doesn’t this violate user story #9 which asks that the user should be able to enter a number of any length for calculation?
Use the article as reference only and follow the user stories provided by Project details page on FCC.