body:before {
    content: "";
    position: absolute;
    background: #000 url(../img/backgrounds/dc-11.jpg);
    background-size: cover;
    z-index: -1; /* Keep the background behind the content */
    height: 20%;
    width: 20%; /* Using Glen Maddern's trick /via @mente */

    /* don't forget to use the prefixes you need */
    transform: scale(5);
    transform-origin: top left;
    filter: blur(0.5px);
}

#bodyDarken {
    position: fixed;
    top: 0;
    bottom: 0;
    width: 100%;
    height: 100%;
    background-color: #000;
    opacity: 0.5;
    z-index: -1;
}