(1) remove background repeat : background-repeat: no-repeat; for the body
(2) background color :hsl(225, 100%, 94%); for the body
(3) background color : white; for the card
i hope that will help u :)
Thank you very much for that advice, and I have already applied those tips. You can see them here and give me a review on them https://www.frontendmentor.io/solutions/qrcodecomponentmain-uh1bAIMHZ8