QR code component using CSS and Bootstrap

What are you most proud of, and what would you do differently next time?

I have started to learn frontend programming and after i finished the courses of HTML and CSS, i started to learn bootstrap and practice it with amazing frontend editor. I hope that I could share all the files correctly and in OK.

What challenges did you encounter, and how did you overcome them?

I did not know what github was until I started this project.

What specific areas of your project would you like help with?

I am new to bootstrap. I do not know when or where I should bootstrap class or not. For example, I did not know that bootstrap has only spefic librariy for color. My question is When using bootstrap, when or where should I use style class in css?