ok so this one is easier but anyways this is how to do it:
find image (usually right click > copy image address)
then type this in:
body {
background-image: url("link");
}
type(or copy) the link to the image(image address) into the place where it says: link
update:
to make it work cooler do this:
body {
background-image: url("link");
background-repeat: no-repeat;
background-position: center;
background-attachment: fixed;
}
type(or copy) the link to the image(image address) into the place where it says: link
(my current background like (copy address): https://art.ngfiles.com/images/1785000/1785693_demoprofile_please-ignore-this.png?f1619773342)