title: How to add image background to btn-default twitter-bootstrap button?
body: <p>I try to design a bootstrap v3.3.5 button by using the existing class <strong>btn-default</strong>, below are the sample of codes of what I had done.</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="false" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;!-- Latest compiled and minified CSS --&gt;
  &lt;link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css"&gt;
  
  &lt;!-- Optional theme --&gt;
  &lt;link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap-theme.min.css"&gt;
  
  &lt;!-- Latest compiled and minified JavaScript --&gt;
  &lt;script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js"&gt;&lt;/script&gt;
  
  
  &lt;style type="text/css"&gt;
    .sign-in-facebook
    {
      background-image: url('http://i.stack.imgur.com/e2S63.png');
      background-position: -9px -7px;
      background-repeat: no-repeat;
      background-size: 39px 43px;
      padding-left: 41px;
      color: #000;
    }
    .sign-in-facebook:hover
    {
      background-image: url('http://i.stack.imgur.com/e2S63.png');
      background-position: -9px -7px;
      background-repeat: no-repeat;
      background-size: 39px 43px;
      padding-left: 41px;
      color: #000;
    }
  &lt;/style&gt;
  &lt;p&gt;My current button got white background&lt;br/&gt;
  &lt;input type="button" value="Sign In with Facebook" class="btn btn-default sign-in-facebook" style="margin-top:2px; margin-bottom:2px;" &gt;
  &lt;/p&gt;
  &lt;p&gt;I need the current btn-default style like below&lt;br/&gt;
  &lt;input type="button" class="btn btn-default" value="Sign In with Facebook" /&gt;
  &lt;/p&gt;
  &lt;strong&gt;NOTE:&lt;/strong&gt; facebook icon at left side of the button.</code></pre>
  </div>
  </div>
  </p>
  
  <p>Sample facebook icon:</p>
  
  <p><img src="https://i.stack.imgur.com/e2S63.png" alt="Sample fb-icon"></p>
  
  <p>How I can modify the class of <code>.sign-in-facebook</code> to create my own style button ?</p>