Mobile first QR component

Replace<div class="container">with the main tag and <div class="attribution"> with the footer tag to fix the accessibility issues. click here for more on web-accessibility and semantic html

There is no need to give the body a width and margin values, to center .container on the page using flexbox or grid, add min-height:100vh; display: flex; align-items: center: justify-content: center; or min-height:100vh; display: grid place-items: center to the body.

USING FLEXBOX:
body{
min-height: 100vh;
display: flex;
align-items: center;
justify-content: center;
}

USING GRID:
body{
min-height: 100vh;
display: grid;
place-items: center;
}

For a responsive content, give .container a fixed max-width value and padding value for all the sides. max-width:20em/rem which is 320px and padding: 1em/rem which is 16px

Give the img a max-width of 100% for a responsive image and a border-radius value m the rest are no needed

Give h1 and p the same font-size of 15px which is 0.9375rem, text-align: center,the same margin-left, margin-right and margin-top values. Give p a margin bottom value.

Use relative units like rem or em as unit for the padding, margin, width values and preferably rem for the font-size values, instead of using px which is an absolute unit. For more on CSS units Click here

Hope am helpful.

Well done for completing this challenge. HAPPY CODING

Nice work! I'd suggest doing NFT Card Challenge as next, this could be nice addition, as there is a task of making an overlay effect on the card. You can practice hover effects by manipulating opacity:0 and opacity: 1 there.

Hope you find this feedback helpful!