html {

    background-image: url();

    overflow: hidden;

}

.overlay {

    position:fixed;

    top:0;

    left:0;

    right:0;

    bottom:0;

    background-image: url(http://www.imagemagick.org/Usage/anim_mods/glitter_blue_tiled.gif);

    opacity: 0.5;

    pointer-events: none;

    z-index:9999;

}