Qr code component using custom css

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

I'll try to use tailwindcss next time.

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

I struggled a bit with placing the component vertically on center with flex, so I just opted to use transform instead.

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

I managed to understand a bit of at least everything that I used when I wrote this one. But one thing I really struggle to understand is the assigning of values to the sizes. What sizes should I use (px, vh, rem, em)? What are their differences and what is the best practice when assigning these values?