body {
    background-image: url('https://cfi.iitm.ac.in/elec-club/images/10bd4.jpg');
    background-attachment: fixed;
}

@media only screen and (max-width: 748px){
    .showbig{
        display:none;
    }
    
}

@media only screen and (min-width: 748px){
    .showsmall{
        display:none;
    }
    
}