title: sizing the input only on xs screens
body: <p>I am adding the class <code>input-lg</code> but I only want it on <code>xs</code> screens and not on <code>md lg</code> screens</p>
  
  <pre><code>&lt;input class="form-control input-lg" type="text"&gt;
  </code></pre>
  
  <p>is there a way to do that using bootstrap only.</p>
  
  <p><em>I think @media queries are the only solution.</em></p>