Calculator App, keyboard friendly

I learned a lot from this project. First of all, I had some issues with the theme switcher. Didn't know what the best approach is so I had to investigate and read a lot of articles but eventually I got there. Also added 'prefers-color-scheme' which sets theme depending on users operating system setting or user agent setting.

Calculator logic in JS was also a lot of work. I am proud of successfully adding user input to the calculator. So u can do all operations with just a keyboard. Also added 'toLocaleString' which I encountered for the first time. It's a nice hack to separate numbers with commas to make it look like a real calculator.

Overall it was a challenging project and I had a lot of fun working on it! :)

If anyone wants to check this calculator out, and leave some comments, it would be awesome!