title: reactjs create-react-app bootstrap4 card not rendering correctly
body: <p>I'm trying to use bootstrap4 with create-react-app. I realized bootstrap.min.css was missing so I put the following line in index.html in the public folder</p>
  
  <pre><code>&lt;head&gt;
  &lt;link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/css/bootstrap.min.css" 
  integrity="sha384-rwoIResjU2yc3z8GV/NPeZWAv56rSmLldC3R/AZzGRnGxQQKnKkoFVhFQhNUwEyJ"
  crossorigin="anonymous"&gt; 
  </code></pre>
  
  <p>I tried using a card and the colors were missing.</p>
  
  <pre><code>        &lt;div className="card card-inverse card-primary mb-3 text-center"&gt;
              &lt;div className="card-block"&gt;
                  &lt;blockquote className="card-blockquote"&gt;
                      React.js
                  &lt;/blockquote&gt;
              &lt;/div&gt;
          &lt;/div&gt;
  </code></pre>
  
  <p>If I then typed a letter in the  like</p>
  
  <pre><code>&lt;head&gt;s
  &lt;link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/css/bootstrap.min.css" 
  integrity="sha384-rwoIResjU2yc3z8GV/NPeZWAv56rSmLldC3R/AZzGRnGxQQKnKkoFVhFQhNUwEyJ"
  crossorigin="anonymous"&gt;
  </code></pre>
  
  <p>The the card color would show. If I then remove the letter and hit save the color disappeared. What is going on here?</p>