body {
    font-family: Arial, sans-serif;
    display: flex;
    justify-content: center;
    align-items: center;
    flex-direction: column;
    height: 100vh;
    margin: 0;
    background-image: url("../img/bg-desktop.png");
    background-size: cover;
    background-attachment: fixed;
}

@media only screen and (max-width: 800px) {
    body {
        background-image: url("../img/bg-mobile.png");
    }
}