QR code component

Hi, great job with the solution.

I just wanted to leave some tips:

• Instead of fixing the height of body to 100vh, is better to set the min-height to 100vh. This makes the layout more dynamic and kind of ready for future changes
• You can use line-height with 1.4 instead of 140%, for example. Not exactly a best-practice, but is more common this way and it is a bit cleaner
• Inside a flexbox, margins "pushes" spaces as possible, so to center .card-container inside body, you could:

body {
  display: flex;
}
.card-container {
  margin: auto; /* This pushes spaces in all four directions and centers the element inside the parent */
}

• This is something I personally think is a better practice, but nothing wrong if you don't want to: using box-sizing: border-box in whole stylesheet

looks pretty good on various screen types.