title: How does Impress.js's CSS work?
body: <p>I was reading about <a href="https://github.com/bartaz/impress.js" rel="nofollow">Impress.js</a> and I have some questions about the code below (Part of the Inpress's demo).</p>
  
  <pre><code>.impress-enabled .step {
      margin: 0;
      opacity: 0.3;
  
      -webkit-transition: opacity 1s;
      -moz-transition:    opacity 1s;
      -ms-transition:     opacity 1s;
      -o-transition:      opacity 1s;
      transition:         opacity 1s;
  }
  
  .impress-enabled .step.active { opacity: 1 }
  </code></pre>
  
  <p><strong>My questions:</strong></p>
  
  <ol>
  <li><p>What is .impress-enabled  class here for?</p></li>
  <li><p>So class .active is applied on the step currently displayed? And thus, its opacity changes to 1 when its displayed and back to .3 when its next one is displayed; as described in .impress-enabled .step above it, right?</p></li>
  </ol>
  
  <p>Thanks for help</p>