CSS
body {
position: absolute;
top: 0;
bottom: 0;
left: 0;
right: 0;
background: url(http://lorempixel.com/420/255) no-repeat center center fixed;
background-size: cover;
}
body:before {
left: 0;
right: 0;
margin-left:auto;
margin-right:auto;
content: "";
position: absolute;
height: 100%;
width: 500px;
background: url(http://lorempixel.com/420/255) no-repeat center center fixed;
background-size: cover;
z-index: -1;
filter: blur(5px);
-webkit-filter: blur(5px);
}
div {
height: 100%;
width: 450px;
margin: 0 auto;
}