Just asking but what is this meant to do exactly

DittoTheDino

Since it looks like it's meant to be a background but it does nothing, so I would recommend using instead of #demo, do

html {
background: transparent url("https://img5.goodfon.com/wallpaper/big/6/91/devushka-fon-vzgliad-rozy.jpg") repeat 100% 100%;
background-size: cover;
background-repeat: no-repeat
}

Don't worry about the global thing, that's just there for the people in charge, you can still upload it, I'm pretty sure.