.parallax-demo {
    position: relative;
    background-size: cover;
    background-position: 50% 50%;
    background-attachment: fixed;
    z-index: 9;
    overflow: hidden;
}

.parallax-demo:after {
    content: '';
    display: block;
    width: 100%;
    height: 100%;
    position: absolute;
    top: 0;
    left: 0;
    z-index: -1;
    background-color: rgba(0,0,0,.1);
}
.parallax-demo h2 {
    position: absolute;
    top: 50%;
    left: 0;
    width: 100%;
    text-align: center;
    transform: translate(0, -50%);
    font-size: 60px;
    color: #fff;
}