html , body{
  height: 100%;
  position: relative;
}

* html .layer_board_bg,
* html .layer_board {
  position: absolute;
}
.layer_board_bg{
  display:none;
  position: fixed;
  width: 100%;
  height: 100%;
  z-index: 1000;
  top: 0;
  left: 0;
  cursor: pointer;
  background: rgba(0,0,0,.5);
}
.layer_board{
  display:none;
  position: fixed;
  text-align: center;
  z-index: 2000;
}