title: z-index still getting covered
body: <p>I'm having a little problem with my footer showing on top of my main content window.</p>
  
  <p>Trying to move the margins so the main content over laps the header by 100px an over laps the footer by 100px and renders to bottom of window.</p>
  
  <p>Not really sure whats wrong could it be to do with "::before" if so is there another way to do this?</p>
  
  <p>Thanks</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-css lang-css prettyprint-override"><code>#wrapper:before {
    content: '';
    float: left;
    height: 100%;
  }
  
  #wrapper {
    height: 100%;
    background-color: black;
  }
  
  #header {
    z-index: 1;
    height: 250px;
    text-align: center;
    background: url(../images/bg02.jpg);
    border-bottom: 10px solid #01A9DC;
  }
  
  #main {
    z-index: 2;
    margin: -100px auto -50px auto;
    width: 80%;
    background-color: white;
    min-height: 400px;
  }
  
  #footer {
    z-index: 1;
    border-top: 10px solid #01A9DC;
    background: url(../images/bg02.jpg);
  }
  
  #footer:after {
    z-index: 1;
    content: '';
    display: block;
    clear: both;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div id="wrapper"&gt;
  
    &lt;div id="header"&gt; HEADER&lt;br&gt; &lt;/div&gt;
  
    &lt;div id="main"&gt; MAIN CONTENT &lt;/div&gt;
  
    &lt;div id="footer"&gt;&lt;/div&gt;
  
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>