CSS Help

Heres One This Is What I Used For My CSS Background :

@import url(https://sophiezhng.github.io/my-space-windows-93-themes/modern.css);

Heres A Site With More Of Them :(https://sophiezhng.github.io/my-space-windows-93-themes)

body{
background-image:url(put image url here);
background-attachment: fixed;
}

background-attachment: fixed; makes the background stay where it is.
an easy thing you can do is look up what you want the background to be and add 1920x1080,
or if you want a pattern, you can look up "repeating ___ background, like this one: http://1-background.com/images/clouds/clouds-fluffly-clouds-seamless-background-blue-sky.jpg