Check out example codes for "how to make a pop up window when clicked on a button". It will help you in understanding the concepts better.

Code Example 1

// When the user clicks on <div>, open the popup
function myFunction() {
  var popup = document.getElementById("myPopup");
  popup.classList.toggle("show");
}

Code Example 2

/* Popup container */
.popup {
  position: relative;
  display: inline-block;
  cursor: pointer;
}

/* The actual popup (appears on top) 
*/
.popup .popuptext 
{
  visibility: hidden;
  width: 
160px;
  background-color: #555;
  color: #fff;
  text-align: center;
  border-radius: 6px;
  padding: 8px 0;
  position: absolute;
  z-index: 1;
  bottom: 125%;
  left: 50%;

    
margin-left: -80px;
}

/* Popup arrow */
.popup .popuptext::after {
  content: "";

    position: absolute;
  
top: 100%;
  left: 50%;
  margin-left: -5px;
  border-width: 5px;
  border-style: solid;

    border-color: #555 transparent 
transparent transparent;
}

/* 
Toggle this class when clicking on the popup container (hide and show the 
popup) */
.popup .show {
  
visibility: visible;
  -webkit-animation: 
fadeIn 1s;
  animation: fadeIn 1s
}

/* Add animation (fade in the popup) */

@-webkit-keyframes fadeIn {
  from {opacity: 0;} 
  to {opacity: 1;}
}


@keyframes fadeIn {
  from {opacity: 0;}
  
to {opacity:1 ;}
}

Code Example 3

<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<style>
/* Popup container - can be anything you want */
.popup {
  position: relative;
  display: inline-block;
  cursor: pointer;
  -webkit-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
  user-select: none;
}

/* The actual popup */
.popup .popuptext {
  visibility: hidden;
  width: 160px;
  background-color: #555;
  color: #fff;
  text-align: center;
  border-radius: 6px;
  padding: 8px 0;
  position: absolute;
  z-index: 1;
  bottom: 125%;
  left: 50%;
  margin-left: -80px;
}

/* Popup arrow */
.popup .popuptext::after {
  content: "";
  position: absolute;
  top: 100%;
  left: 50%;
  margin-left: -5px;
  border-width: 5px;
  border-style: solid;
  border-color: #555 transparent transparent transparent;
}

/* Toggle this class - hide and show the popup */
.popup .show {
  visibility: visible;
  -webkit-animation: fadeIn 1s;
  animation: fadeIn 1s;
}

/* Add animation (fade in the popup) */
@-webkit-keyframes fadeIn {
  from {opacity: 0;} 
  to {opacity: 1;}
}

@keyframes fadeIn {
  from {opacity: 0;}
  to {opacity:1 ;}
}
</style>
</head>
<body style="text-align:center">

<h2>Popup</h2>

<div class="popup" onclick="myFunction()">Click me to toggle the popup!
  <span class="popuptext" id="myPopup">A Simple Popup!</span>
</div>

<script>
// When the user clicks on div, open the popup
function myFunction() {
  var popup = document.getElementById("myPopup");
  popup.classList.toggle("show");
}
</script>

</body>
</html>

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