code to use for gif backgrounds

i'm sure this'll work with regular images too however this is what i had to use to get the background in this blog https://blog.spacehey.com/entry?id=21394 to work albeit it is a bit grainy since the gif was small to begin with (edit: appears this code only works on blog posts not bulletins)

<style>

body{
    background-image: url('img url');
    background-size: cover;
    
    
    
    height: 100vh;
    padding:0;
    margin:0;
} </style>