#old-banner-button {
    width:100%;
}

#old-banner-button img {
    margin: 80px auto;
    width:100%;
}

#old-banner-button img.img-mobile {
    max-width:300px;
} 

#old-banner-button img.img-desktop {
    display:none;
    
}   

@media screen and (min-width: 900px) {
    #old-banner-button img.img-mobile {
        display:none;
    } 
    #old-banner-button img.img-desktop {
        display:block;
        max-width:700px;
    } 
}