title: center an id in a html page using css
body: <p>this is my code:</p>
  
  <pre><code>   &lt;div id="content"&gt;   
          &lt;div id="slider1"&gt;
              &lt;div class = "content-dir"&gt;
                    &lt;h1&gt;Anno 2012&lt;/h1&gt;
              &lt;/div&gt;
          &lt;/div&gt;
      &lt;/div&gt;
  </code></pre>
  
  <p>I would center <code>slider1</code>. I used <code>margin: 0 auto</code> but it didn't work.</p>
  
  <p>The style applied to id <code>content</code> is only <code>height</code></p>