Responsive QR Code Page using CSS Flexbox and CSS variables

Replace<div class="container">with the main tag, <h2> 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 .container on the page using flexbox only instead of flexbox and margin, add justify-content: center to the body and remove the margin value in .container.

Give the img a max-width of 100%.

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