<link href="//maxcdn.bootstrapcdn.com/bootstrap/3.3.0/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css"> <script src="//maxcdn.bootstrapcdn.com/bootstrap/3.3.0/js/bootstrap.min.js"></script> <script src="//code.jquery.com/jquery-1.11.1.min.js"></script> <!------ Include the above in your HEAD tag ----------> <div class="container"> <div class="row"> <h2>Create your snippet's HTML, CSS and Javascript in the editor tabs</h2> <img class="visible-lg" src="http://scottjehl.github.io/picturefill/examples/images/extralarge.jpg" width="768" height="1024" alt="" title="File size= 750KB"> <img class="visible-md" src="http://scottjehl.github.io/picturefill/examples/images/large.jpg" width="480" height="640" alt="" title="File size= 355KB"> <img class="visible-sm" src="http://scottjehl.github.io/picturefill/examples/images/medium.jpg" width="375" height="500" alt="" title="File size= 239KB"> <img class="visible-xs" src="http://scottjehl.github.io/picturefill/examples/images/small.jpg" width="180" height="240" alt="" title="File size= 55KB"> </div> </div>