Responsive Youtube.txt

First method is try http://embedresponsively.com/
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Second Method
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CSS

.video-container {
  position: relative;
  padding-bottom: 56.25%; /*16:9*/
  padding-top: 30px; 
  height: 0; 
  overflow: hidden;
}
 
.video-container iframe,
.video-container object,
.video-container embed {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
}

.video-container {
position: relative;
padding-bottom: 56.25%;
padding-top: 30px; height: 0; overflow: hidden;
}

HTML
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<div class="video-container"><iframe width="853" height="480" src="https://www.youtube.com/embed/z9Ul9ccDOqE" frameborder="0" allowfullscreen</iframe</div>