html, body {
    height: 100%;
    min-height: 100vh;
    width: 100vw;
    margin: 0;
    padding: 0;
}

body {
    background-image: url('../img/default-bg.png'); /* or your desired image */
    background-size: cover;
    background-position: center center;
    background-repeat: no-repeat;
    /* background-attachment: fixed; */
    min-height: 100vh;
    width: 100vw;
    overflow-x: hidden;
}