title: paper-menu don't display on foreground
body: <p>I have this problem:</p>
  
  <p><a href="https://i.stack.imgur.com/BKL5i.gif" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/BKL5i.gif" alt="weird"></a></p>
  
  <p>When I visit page the paper-menu displays correctly but when i scroll down and back to top, the paper-menu is behind the div (with id nav). I tried to play with z-index and positons but nothing worked.</p>
  
  <p>CSS:</p>
  
  <pre><code>paper-scroll-header-panel {
    position: absolute;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
    background-color:  #eee;
  }
  
  paper-toolbar {
    /* custom toolbar height */
    height: 100px;
    background-color: #6a1b9a;
    overflow: visible;
  }
  #nav {
    background-color: #6a1b9a;
  }
  </code></pre>
  
  <p>HTML:</p>
  
  <pre><code>&lt;paper-scroll-header-panel condenses keep-condensed-header header-height="100" condensed-header-height="50"&gt;
  
    &lt;paper-toolbar&gt;
  
     &lt;h1&gt;Some text&lt;/h1&gt;
      &lt;div class="flex"&gt;&lt;/div&gt;
      &lt;paper-menu-button&gt;
        &lt;paper-icon-button icon="menu" class="dropdown-trigger"&gt;&lt;/paper-icon-button&gt;
        &lt;paper-menu class="dropdown-content"&gt;
          &lt;paper-item&gt;Share&lt;/paper-item&gt;
          &lt;paper-item&gt;Settings&lt;/paper-item&gt;
          &lt;paper-item&gt;Help&lt;/paper-item&gt;
        &lt;/paper-menu&gt;
      &lt;/paper-menu-button&gt;
  
     &lt;div id="nav" class="flex bottom fit"&gt;
              &lt;paper-tabs noink  &gt;
                &lt;paper-tab &gt;Tab1&lt;/paper-tab&gt;         
                &lt;paper-tab &gt;Tab2&lt;/paper-tab&gt;
                &lt;paper-tab &gt;Tab3&lt;/paper-tab&gt;
                &lt;paper-tab &gt;Tab4&lt;/paper-tab&gt;
              &lt;/paper-tabs&gt;
    &lt;/div&gt;
  
    &lt;/paper-toolbar&gt;
  
    &lt;div class="content"&gt;
  
      &lt;sample-content size="100"&gt;&lt;/sample-content&gt;
  
    &lt;/div&gt;
  
  &lt;/paper-scroll-header-panel&gt;
  </code></pre>
  
  <p><a href="http://roadiction.com/bower_components/paper-scroll-header-panel/demo/demo8.html" rel="nofollow noreferrer">If you want to play around with code...</a> (I don't know how to import polymer to jsbin or codepin. It says something about no third party using.)</p>