.layer_hidden {
  display: none;
}

.layer_visible {
  display: block;
}
iframe#listbox_backalpha {
  position :absolute;
  left: 0px;
  top: 0px;
  width: 100%;
  height: 100%;
  z-index: 97;
  filter: alpha(opacity=10);
  -moz-opacity:0.10;
  opacity:0.10;
}

div#listbox_layeralpha {
  position :absolute;
  left: 0px;
  top: 0px;
  width: 100%;
  height: 100%;
  z-index: 98;
  background: #550000;
  filter: alpha(opacity=50);
  -moz-opacity:0.50;
  opacity:0.50;
}