README.md

To use this put in your html document:
<script type="text/javascript" src="https://is.gd/popupjs"></script>
and
<link rel="stylesheet" href="https://is.gd/popupcss">
Then, call popup() with the args as html code that you want to be in the popup.

popup.css

.modal {
    display: none; /* Hidden by default */
    position: fixed; /* Stay in place */
    z-index: 1; /* Sit on top */
    padding-top: 100px; /* Location of the box */
    left: 0;
    top: 0;
    width: 100%; /* Full width */
    height: 100%; /* Full height */
    overflow: auto; /* Enable scroll if needed */
    background-color: rgb(0,0,0); /* Fallback color */
    background-color: rgba(0,0,0,0.4); /* Black w/ opacity */
}

/* Modal Content */
.modal-content {
    background-color: #fefefe;
    margin: auto;
    padding: 20px;
    border: 1px solid #888;
    width: 80%;
}

/* The Close Button */
.close {
    color: #aaaaaa;
    float: right;
    font-size: 28px;
    font-weight: bold;
}

.close:hover,
.close:focus {
    color: #000;
    text-decoration: none;
    cursor: pointer;
}

popup.js

function popup(content){
var modal = document.createElement('popup');

//create x
var span = document.createElement("close")[0];
span.innerHTML = '×';
modal.appendChild(span)

// When the user clicks the button, open the modal 
modal.style.display = "block"

// When the user clicks on <span> (x), close the modal
span.onclick = function(){modal.style.display = "none"}

// When the user clicks anywhere outside of the modal, close it
window.onclick = function(event) {
  if (event.target == modal) {
    modal.style.display = "none";
  }
}
document.body.appendChild(modal)
}