QR Code Component Using CSS Flexbox

I've just completed a front-end coding challenge from @frontendmentor!

You can see my solution here: https://www.frontendmentor.io/solutions/qr-code-component-using-css-flexbox--7m30nF8si

Any suggestions on how I can improve are welcome!

PS:

I usually find it a bit difficult on the following things:

1. Center/Position stuff.

2. Setting Height/Width and stuffs of images

So would want some advice to improve on that

Thank you