Calculator exercise

Js and css code is a little scuffed probably a bit of repeat and unnecessary code written, wasn't too sure whether to change the class or js style attributes so I just did attributes so there is a big clump of code for the different themes down the bottom. I couldn't figure out how to format to 100,000 I got close though ahah. also i didnt know how to change hover color in js, I assume the way around it was to set an event listener for mouse over and have it set that way. Give me some criticism