title: Div inside others (with margin-top) is pushing parents down
body: <p>When I was working on a little project I ran into a delema I can't for the life of me figure out. Why is it that the div inside <strong>#appHead</strong> is causing <strong>#windowBody</strong> to move down? Any Ideas?</p>
  
  <pre><code>&lt;html&gt;
      &lt;head&gt;
          &lt;meta http-equiv="Content-Type" content="text/html; charset=UTF-8"&gt;
          &lt;title&gt;Atlas - Valencia College&lt;/title&gt;
          &lt;meta charset="utf-8"&gt;
          &lt;link rel="stylesheet" href="styles.css" type="text/css"&gt;
          &lt;!--&lt;script type="text/javascript" src="scripts.js"&gt;&lt;/script--&gt;
      &lt;/head&gt;
      &lt;body&gt;
          &lt;div id="bgGrad"&gt;&lt;/div&gt;
          &lt;div id="windowTop"&gt;
          &lt;/div&gt;
          &lt;div id="windowBody"&gt;
              &lt;div id="appEnv"&gt;
                  &lt;div id="appHead"&gt;
                      &lt;div style="margin-top:20px;height:20px;"&gt;&lt;/div&gt;
                  &lt;/div&gt;
              &lt;/div&gt;
          &lt;/div&gt;
          &lt;div id="windowFoot"&gt;
          &lt;/div&gt;
      &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>css</p>
  
  <blockquote>
    <p>body{
          background:url("lol.png");
          margin:0;
        }
        #appEnv{
          width:100%;
          height:100%;
          top:0;
          bottom:0;
          left:0;
          right:0;
          outline:dotted 1px blue; 
        }
        #appHead{
          height:100px;
        }
        #windowBody{
          position:absolute;
          top:0;
          width:100%;
          bottom:0;
        }</p>
  </blockquote>
  
  <p>Even when I removed all of the absolute positioning, it was still the case, however I may have done it wrong.</p>