body {
    background-image: url(https://santuariosdealtura.cl/background-xs.jpg);
    background-position: 50%;
    background-repeat: no-repeat;
    background-attachment: fixed;
    background-size: cover;
    background-color: #464646
}

@media(min-width: 768px) {
    body {
        background-image:url(https://santuariosdealtura.cl/background-sm.jpg)
    }
}

@media(min-width: 992px) {
    body {
        background-image:url(https://santuariosdealtura.cl/background-md.jpg)
    }
}

@media(min-width: 1200px) {
    body {
        background-image:url(https://santuariosdealtura.cl/background-lg.jpg)
    }
}