Tristate-theme calculator with keyboard functionality using CSS Grid

1. Is there any easier way to implement the theme functionality? It's what I struggled with the most.

2. Whenever using the dev tools to test my website's functionality on mobile devices, everything looks and works great, but when I open it on my actual mobile device, the buttons are larger than they're meant to be and are skewed outside of the keypad (container). Is there anyway to fix this?

3. Also on mobile, typing the same button twice (for instance, typing 77), it zooms in. Is there anyway to fix this as well?

Thank you for your help!