Mobile first with Vanilla JS functionalities

Hi! Working on other challenges made me realise that I need to work on my JS skills quite a lot, so I decided to include it where I can.

I added some JS functionalities here (it's just a skeleton, really, but you can play with it in the console - more info in readme).

I would like to get some feedback on accessibility - I added custom focus styles and aria-labels to the buttons since they've got no text, but not sure how to handle the main component, should anything be added there?

If you spot any issues, let me know! Thanks :)