[CSS help, kinda dumb idk] loading

um i was wondering...
in some accounts ive seen a big image appears the whole screen before to see the account.
in the "win05 css" (https://github.com/myspace93/myspace93.github.io) it had an loading screen, i remember because i was playing with css's a long time ago
so if someone know the code or a css with this, can you show me? thx