QR Code Component using BEM

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

I am proud of my usage of the BEM in my CSS as it structures everything cleanly. Next time, I want to try to use CSS Sass, so I can remove some redundant code.

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

One challenge I encountered was moving the image to the center of the card. I overcame it by using padding on the card.

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

1. I would like to know if my usage of the HTML5 semantic is used correctly.
2. I would like to know if my QR code component is responsive.
3. I would like to know if using REM (instead of REM) through my CSS is a good idea. If it is not, what parts of my design require the px instead of REM? 3A. When is using PX better than using REM (in general and in the case of the QR Code)?
4. Am I using the BEM structure right?