CSS modal

<style>

/* The Modal (background) */
.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;
}
</style>

<!-- Trigger/Open The Modal --> 
<button id="myBtn">Open Modal</button> 

<!-- The Modal --> 
<div id="myModal" class="modal"> 
<!-- Modal content --> 

<div class="modal-content"> 
<span class="close">&times;</span> 
<p>Some text in the Modal..</p> 

</div> 
</div>

<script> 

// Get the modal 
var modal = document.getElementById("myModal"); 

// Get the button that opens the modal 
var btn = document.getElementById("myBtn"); 

// Get the <span> element that closes the modal 
var span = document.getElementsByClassName("close")[0]; 

// When the user clicks the button, open the modal 
btn.onclick = function(){ 
    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"; 
   } } 

</script>