footer.css

html,
body {
    height: 100%;
    margin: 0;
}

.contenuto {
    padding: 90px 50px 0px 50px;
    min-height: 100%;
}

footer,
.push {
    margin-top: 30px;
    width: 100%;
    height: 150px;
    vertical-align: center;
    background: black;
    color: white;
}


/* centro verticalmente gli elementi del footer */

footer .center {
    display: flex;
    align-items: center;
    justify-content: center;
}


/* adatto l'altezza del footer per i dispositivi mobili */

@media only screen and (max-width: 768px) {
    footer,
    .push {
        margin-top: 30px;
        width: 100%;
        height: 400px;
        vertical-align: center;
        background: black;
        color: white;
    }
    .contenuto {
        padding: 90px 20px 0px 20px;
        min-height: 100%;
    }
}

.navbar {
    background-color: black;
}