title: Centred element off-centre after php
body: <p>I'm getting a really confusing positioning problem. I have an <code>&lt;img&gt;</code> element with 
  <code>display:block;margin-left:auto;margin-right:auto;</code>, which ought to centre it. The problem is that it's not centred within its container, but rather appears to be centred within the left half of its container.</p>
  
  <p>Complicating matters, this only occurs following a linked php file </p>
  
  <pre><code>&lt;div class="header"&gt;
  ...
  &lt;nav id="menu" class="topnav"&gt;
  &lt;ul&gt;
      &lt;li&gt;&lt;a class="navlink" href="alexandria.html"&gt;&lt;br style="clear: both;"/&gt;Alexandria&lt;br style="clear: both;"/&gt;&lt;span&gt;Referencing Manager&lt;/span&gt;&lt;/a&gt;&lt;/li&gt;
      &lt;li&gt;&lt;a class="navlink" href="ceryneian.html"&gt;&lt;br style="clear: both;"/&gt;Ceryneian&lt;br style="clear: both;"/&gt;&lt;span&gt;Research Browser&lt;/span&gt;&lt;/a&gt;&lt;/li&gt;
      &lt;li&gt;&lt;a class="navlink" href="blog"&gt;&lt;br style="clear: both;"/&gt;Blog&lt;br style="clear: both;"/&gt;&lt;span&gt;Thoughts&lt;/span&gt;&lt;/a&gt;&lt;/li&gt;
      &lt;li&gt;&lt;a class="navlink" href="about.html"&gt;&lt;br style="clear: both;"/&gt;About&lt;br style="clear: both;"/&gt;&lt;span&gt;Our Team&lt;/span&gt;&lt;/a&gt;&lt;/li&gt;
  &lt;/ul&gt;
  &lt;/nav&gt;
  </code></pre>
  
  <p> - if I remove this it works fine. <strong>Edit</strong> I've been testing my CSS, and it appears that if I remove the <code>float:right;</code> on the <code>&lt;ul&gt;</code>it works - I don't know why though, and I want to keep the float if possible.</p>
  
  <p>Here's the page in question <a href="http://fireoak.3owl.com/404.html" rel="nofollow">http://fireoak.3owl.com/404.html</a> - thanks in advance if you can be of any assistance.</p>