title: Make a div responsive width/height in bootstrap 3
body: <p>I have an image container with an image. The size is 317x242px. I placed the <code>image-container</code> inside a <code>col-md-3</code> div. The width is a little bit larger in bootstrap, not exactly 317px, but it's not problem, because I'm using <code>background-size:cover</code> to fill the whole div.</p>
  
  <p>How is it possible to keep the dimension, if the width smaller/higher than 317px?</p>
  
  <p><a href="http://www.bootply.com/6waABmJhuL" rel="nofollow">http://www.bootply.com/6waABmJhuL</a></p>