*{margin:0;padding:0;}
.mask{
  position: fixed;
  top:0;
  right:0;
  bottom:0;
  left:0;
  z-index: 1;
  background: rgba(0,0,0,0.4);
  display:none;
}
.box{
  background: #fff;
  z-index: 2;
  position: fixed;
  bottom:0;
  left:0;
  right:0;
  height: 55vh;
  display:none;
}