#mask {
background-repeat: no-repeat;
background-position: center;
position: fixed;
top: 0;
left: 0;
width: 100%;
height: 100%;
z-index: -1;
background-color: rgba(0, 0, 0, 0);
.blur & {
z-index: 100;
background-color: rgba(0, 0, 0, .25);
}