Calculator app using grid and SCSS

I had problems centering the calculator vertically on small screens. Using 100svh didn't work, so I finally used Javascript to determine the user's window height. Is there a good solution in CSS?

Also I am uncomfortable with my code organisation. Should a shorter script like that use classes (or one class) already? And it seems overly complicated. At last I decided to perform the actual calculation inside a while loop do do a chain of arithmetical operation in the right order. Are there any more elegant solutions, e.g. a way to use array methods for this? And if - how?

Thank you for any suggestions!