title: Center with margin auto doesn't work
body: <p>I use a jQuery animation in my page which adds some CSS properties and I don't understand why the <code>margin: auto</code> doesn't work.</p>
  
  <p>The HTML code (with style properties added by jQuery) :</p>
  
  <pre><code>&lt;body style="overflow: hidden;"&gt;
      &lt;div id="tuto_wamp" style="width: 7680px; height: 923px; "&gt;
          &lt;!-- Step 1 --&gt;
          &lt;div style="height: 549px; width: 1280px; margin-top: 0px; margin-left: 0px; position: absolute; overflow-y: hidden; overflow-x: hidden; "&gt;
              &lt;div class="content_tuto"&gt;
                  &lt;img src="images/install1.png" alt=""&gt;
              &lt;/div&gt;
          &lt;/div&gt;
      &lt;/div&gt;
  &lt;/body&gt;
  </code></pre>
  
  <p>My CSS code :</p>
  
  <pre><code>#tuto_wamp 
  { 
      background: #3a393c;
      width: 100%;
  }
  
  .content_tuto
  {
      width: 100%;
      margin: auto;
      display: block;
  }
  </code></pre>
  
  <p>I don't know which property blocks the <code>margin: auto</code> to center the image.</p>
  
  <p>Thank you.</p>