QR Code Solution Using Basic Bootstrap - First Frontend Mentor Problem

Hi everyone!:D Feedback welcome. I'm new to this platform & frontend development isn't exactly my forte, so I'm always looking for ways to improve. I have a few questions:

How do I go about making this site more mobile friendly? (I'm not entirely sure if I implemented that part correctly:V) How do I test my site's mobile-friendliness? (is there a way to display it on my computer as if it were on a phone?) Any tips on organizing/making cleaner code? Should I try using React?