Credit App using CSS FlexBox,Javascript, and HTML!

This project took me about a week. I've been coding for just a little over 3 months now and I would definitely say this tested my current knowledge. This let me know what kind of things I need to be studying more. 1.Media querys- I just could not for the life of me get this to work perfectly. 2.Javascript and CSS refactoring. This was another big one. I got overwhelmed at times just trying to find out the best practice for each other these. 3.Using Javascript more efficiently. What I mean this is that i'm sure there are best practices that im not using when i comes to the way i wrote my Javascript. I'm also pretty sure my code looks a little messy. any feedback to any of these points or if you see something else please let me know. Oh I also used ID's for the DOM because for some reason .getbyElementclass was not working?? If you made it this far thank you for your time! cheers!