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

body {
    min-height: 100vh;
    background-image: url("images/wallpaper.jpg");
    background-size: cover;
    background-position: center center;
    background-repeat: no-repeat;
    background-color: #f5f5f5;
}
@media (max-width: 768px) {
    body {
        background-size: contain;
        background-position: center center;
        background-repeat: no-repeat;
    }
}