My newb solution to the Desktop version (HTML and CSS)

Replace<div class="qr-parent">with the main tag, <p class="head"> with <h1> and <div class="attribution"> with the footer tag to fix the accessibility issues. click here for more on web-accessibility and semantic html

To center .qr-parent on the page using flexbox or grid instead of margin, 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;
}

Give .qr-text a margin value for all the sides, text-align: center and a font-size of 15px which is 0.9375rem, this will be the font-size of both p and h1. Give p a margin-top or h1 a margin-bottom value for the space between the text.

For a responsive content, give .qr-parent a fixed max-width value and increase its padding value. max-width:320px, padding:16px. Give the img a max-width of 100% and a border-radius value, the rest are not needed.

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