JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<head class="no-js">
    <meta http-equiv="Content-type" content="text/html; charset=utf-8">
    <title>Bonzai Rush</title>
    
</head>
<body>
    <h1>Don&rsquo;t get smashed!</h1>
    <div class="container">
        <div class="video">
            <iframe width="960" height="750" src="http://www.youtube.com/embed/5nmOMo4OPi4" frameborder="0" allowfullscreen></iframe>
        </div>
    </div>
</body>

CSS

body {
    padding: 20px;
    margin: 0;
}

.container {
    max-width: 300px;
    background-color: #eee;
    
}

/* 
   Fluid images
   and fallback for embedded media when there's no JavaScript 
   Adapted from:
   http://unstoppablerobotninja.com/entry/fluid-images/
*/
img,
.no-js embed,
.no-js object,
.no-js iframe,
video {
   max-width: 100% !important;
   display: block;
}

/* 
   Intrinsic ratios for videos
   Adapted from: 
   http://www.alistapart.com/articles/creating-intrinsic-ratios-for-video/ 
*/
.vid-container {
   position: relative;
   padding-top: 35px; /* little extra for the player's chrome (esp YouTube) */
}

.vid-container iframe, .vid-container embed, .vid-container object {
   position: absolute;
   top: 0;
   left: 0;
   width: 100%;
   height: 100%;
}

JavaScript

$('html').removeClass('no-js').addClass('js');   

$('object, embed, iframe').each(function(){
      //cache the video
      var vid = $(this),
      //get its width
      vid_width = vid.width(),
      //get the width of its container
      vid_parent_width = vid.parent().width();

      //only if the video is breaking out of its parent...
      if (vid_width > vid_parent_width) {
         
         //get its height
         var vid_height = vid.height(),
         //calculate the aspect ratio as a %
         vid_aspect = vid_height/vid_width * 100 + "%"; 

         //wrap the video in our div.vid-container
         vid.wrap('<div class="vid-container">');

         //set the padding to the aspect ratio as a percentage
         //vid.parent() is now the div.vid-container
         vid.parent().css('padding-bottom', vid_aspect); 

      }

   });