html, body {
    width: 100%;
    height: 100%;
}
body {
    position: relative;
    background-image:url('../img/bg-mobile.jpg');
    background-attachment: fixed;
    background-position: center center;
    background-size: cover;
}
.content-wrap {
    width: 100%;
    height: 100%;
    position: absolute;
    left:50%;
    top:50%;
    transform: translate(-50%,-50%);
    z-index:10;
}
.w {
    position:absolute;
    bottom:0;
    left:0;
    z-index:9;
}
@media (min-width:992px) {    
    body {
        background-image:url('../img/bg.jpg');
    }
}