Submission for QR code component

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

Fitting the image inside the card. It got me thinking for a while. Also, doing a project with the instructions because I've never attempted something like this. Created a readme for the first time:)

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

I was really confused about what to pick b/w px, rem, em but this article https://fedmentor.dev/posts/font-size-px/ really helped me and also gave a perspective of why should we follow a particular workflow.

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

Do I have to calculate size something minor - like {letter-spacing: 0.03em}. Is it okay to have it this way or can I go with px in this one? Also, please give feedback on semantic html or css.