JSFiddle - React, Tailwind, and code Playground

HTML

<button id="watchbutton">Watch Trailer &#9658</button>


<div id="close">
  <div id="trailerdivbox">
    <div class="videoWrapper">
      <iframe id="video" class="trailervideo" width="560" height="315" data-src="https://www.youtube.com/embed/TDwJDRbSYbw" src="about:blank" frameborder="0" allowfullscreen></iframe>
    </div>
  </div>
</div>

CSS

/* Watch Trailer Button CSS */

#watchbutton {
  background-color: #f2f2f2;
  color: red;
  font-weight: 600;
  border: none;
  /* This one removes the border of button */
  padding: 10px 12px;
}

#watchbutton:hover {
  background-color: #e2e2e2;
  cursor: pointer;
}

#trailerdivbox {
  display: none;
  width: 100%;
  height: 100%;
  position: fixed;
  overflow: auto;
  /* Enable Scrolling */
  background-color: rgb(0, 0, 0);
  /* Fallback color */
  background-color: rgba(0, 0, 0, 0.4);
  /* Black w/ opacity */
}

.videoWrapper {
  position: relative;
  padding-bottom: 56.25%;
  /* 16:9 */
  padding-top: 25px;
  height: 0;
}

.videoWrapper iframe {
  position: absolute;
  max-width: 560px;
  max-height: 315px;
  width: 95%;
  height: 95%;
  left: 0;
  right: 0;
  margin: auto;
}

JavaScript

// Get the modal
var modal = document.getElementById('trailerdivbox');

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

function playVideo() {
  var video = document.getElementById('video');
  var src = video.dataset.src;

  video.src = src + '?autoplay=1';
}

function resetVideo() {
  var video = document.getElementById('video');
  var src = video.src.replace('?autoplay=1', '');

  video.src = '';
  video.src = src;
}

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

var trailerbox = document.getElementById("close");

trailerbox.onclick = function() {
  modal.style.display = "none";
  resetVideo();
}

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