// Opacity
@black: rgb(17,17,17);

.opacity(@opacity) {
  opacity: @opacity;
  // IE8 filter
  @opacity-ie: (@opacity * 100);
  filter: ~"alpha(opacity=@{opacity-ie})";
}


.black-filter(@opacity){
    top: 0;
    left: 0;
    height: 100%;
    width: 100%;
    position: absolute;
    background-color: fade(@black,@opacity);
    display: block;
    content: "";
    z-index: 1; 
}