Calculator app ES6 Classes SASS 7-1

Hello everyone.

This was by far the most difficult challenge I have worked on, both in terms of the styling and the calculator logic. I have learned quite a lot! It's the first time that I have used ES6 classes on a Frontend Mentor project, and I found it made the codebase far more manageable.

I've added a few extra little features as well, such as transition smoothing when changing themes and an on-off button.