Tip calculator using JavaScript, CSS grid and flexbox

I watched my JavaScript lecture yesterday and wanted to do something challenging with it so I chose this project. I thought this would relatively be simple but I couldn't have been more wrong. I totally lost count of the number of times I wanted to laugh, cry or scream. It was quite an experience but totally worth it. It left me with this amazing outcome, tons of new JavaScript knowledge and a headache. My JavaScript is a mess but any kind of feedback or suggestion would be highly appreciated. Happy Coding!