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/* Responsive Vimeo Iframe */
.embed-container {
  position: relative;
  padding-bottom: 56.25%;
  height: 0;
  overflow: hidden;
  max-width: 100%;
  iframe,
  object,
  embed {
      position: absolute;
      top: 0;
      left: 0;
      width: 100%;
      height: 100%;
  }
}

<div class="embed-container">
  <iframe src='http://player.vimeo.com/video/VIDEO_ID_HERE' frameborder='0' webkitAllowFullScreen mozallowfullscreen allowFullScreen></iframe>
</div>