.background-image {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    min-height: 100vh;
    background-image: url('background.png');
    background-repeat: repeat-x;
    background-position: center top;
    z-index: -1;
    background-size: 100% auto;
}

@media (max-width: 768px) {
    .background-image {
        position: fixed;
        top: 0;
        left: 0;
        right: 0;
        bottom: 0;
        width: 100%;
        height: 100%;
        background-size: cover;
        background-repeat: no-repeat;
        background-attachment: scroll;
    }
}