.popup {
  margin: 70px auto;
  width: 500px;
  position: relative;
  z-index: 999;
  background: transparent;
}
.overlay{
  position:absolute;
  top:0;
  bottom:0;
  left:0;
  right:0;
  visibility:hidden;
  opacity:0;
  background:transparent;
  z-index: 999;
}
.overlay:target{
  visibility: visible;
  opacity: 1;
}
.window{
  background: white;
  border-right: 1px solid black;
  border-left: 1px solid black;
  border-bottom: 1px solid black;
  border-radius: 0px 0px 15px 15px;
  padding:10px;
  height: 400px;
}
.top{
  background: pink;
  border: 1px solid black;
  height: 50px;
  border-radius: 15px 15px 0px 0px;
}
button{
  width:25px;
  height: 25px;
  border-radius: 5px;
  border: 1px solid black;
  color: black;
  background: white;
}