#popup {
  width:700px;
  display:block;
  position:absolute;
  margin:0 auto;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  z-index: 9999;
}
#close{
  font-size:30px; 
  padding-top:1%; 
    padding-right: 2%;
  margin:auto;
    top:1px;
    right:1px;
  position: absolute;
}

@media (max-width:768px){
  #popup {
    width:350px;
  }
  #close{
    font-size:30px; 
    padding-left:94%;
    padding-top:1%; 
    margin:auto;
    position: absolute;
  }
  }