body {
    background-image: url("https://static.tildacdn.com/tild6337-3765-4666-b262-656534653534/____png_.png");
    background-position: 0 0;
    background-size: cover;
    background-attachment: fixed;
    
    @media screen and (max-width: 900px)
    background-image: url("https://static.tildacdn.com/tild6337-3765-4666-b262-656534653534/____png_.png");
    background-position: 7% 0;
    background-size: cover;
    background-attachment: fixed;
}