button {
   background: #000;
   color: #fff;
   text-align: center;
   font-weight: bold;
   padding: 10px 30px;
   border-radius: 3px;
}

#overlay {
   position: fixed;
   height: 100%; 
   width: 100%;
   top: 0;
   right: 0;  
   bottom: 0;
   left: 0;
   background: rgba(0,0,0,0.8);
   display: none;
}

#popup {
   max-width: 600px;
   width: 80%;
   max-height: 300px;
   height: 80%; 
   padding: 20px;
   position: relative;
   background: #fff;
   margin: 20px auto;
}

#close {
   position: absolute;
   top: 10px;
   right: 10px;
   cursor: pointer;
   color: #000;
}