QR code component

Hey! I am Reza 🙂 I just recently started to learn web-development and would like to get every little help out there. So if you have the time, feel free to look over my project/projects and give me some advice to get better as fast as possible.

Some questions for this "QR-Code" Project:

1. Is my "Index.html" well structured?
2. Did I center everything right, or was there a easier way?
3. What did I do completely wrong, and just have luck within this project?
4. Grid or Flex? Why did i need another grid/center at my last paragraph? Is it because of the individual width?

I appreciate it✌️