Hi! Here's my feedback as a seasoned dev, but a beginner in the frontend:
Nice and clean HTML structure. I wasn't sure about the usage of the article tag, but I've read more on this topic and I think it's fine.
I like the variables you've used in the style.css. I had a problem remembering which color is which, and your solution to that seems very good. Definitely stealing this one for another challenge.
I can see that you've "hardcoded" the card height as well as the width. I think you should only hardcode the width, and let the height be more dynamic.
I can see a small difference between the design and your solution when it comes to the "copy" text ("Scan the QR code..."). I was having the same issue, and I've dealt with that using a Figma design file - this text has non-default line spacing. If you want your solution to be 100% as on the design, check the line spacing there.
Overall, great solution! Definitely better than mine and I've learned some new things from you, so thank you!