на кнопке нажмите видео всплывающее окно в HTML

<html>
<style>
.modal {
  display: none; 
  position: fixed;
  z-index: 1; 
  padding-top: 100px; 
  left: 0;
  top: 0;
  width: 100%;
  height: 100%; 
  overflow: auto;
  background-color: rgb(0,0,0);
  background-color: rgba(0,0,0,0.4); 
}
.modal-content {
  background-color: #fefefe;
  margin: auto;
  padding: 20px;
  border: 1px solid #888;
  width: 80%;
}
.close {
  color: #aaaaaa;
  float: right;
  font-size: 28px;
  font-weight: bold;
}

.close:hover,
.close:focus {
  color: #000;
  text-decoration: none;
  cursor: pointer;
}
</style>
<body>
       <h1>Contents of your page here</h1>
<button id="myBtn">Open Popup</button>

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

  <!-- Modal content -->
  <div class="modal-content">
    <span class="close">&times;</span>
    <video controls>
    <source src="video source here">
    </video>
  </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>

       <h1>(This example works using the modal property in CSS)</h1>

</body>
</html>
Thomas coder