title: pop-up div is hidden under iframe in IE11
body: <p>I've got a div with some text hidden by default. When you click on button, it will apear, but in IE11 (which I got), some part of div is covered under youtube iframe and I don't know, how to repair it :(
  Here is the image of the problem:<br>
  <img src="https://i.stack.imgur.com/2fhcm.png" alt="image of problem"></p>
  
  <p><strong>HTML</strong></p>
  
  <pre><code>&lt;div class="product-spec-wrapper" style="z-index:999;"&gt;
      &lt;div class="product-spec-button"&gt;
          &lt;p&gt;Specifikace produktu&lt;/p&gt;
      &lt;/div&gt;
      &lt;div class="product-spec-holder" style="position:absolute; z-index:1001;"&gt;
          &lt;div class="additional-information-inner"&gt;
              &lt;div class="onajwrap"&gt;
                  &lt;div class="product-spec-content"&gt;
                  //some content here                         
                  &lt;/div&gt;
              &lt;/div&gt;
          &lt;/div&gt;
      &lt;/div&gt;
  &lt;/div&gt;
  
  &lt;div class="entry-content"&gt;
      &lt;div class="clicker"&gt;&lt;/div&gt;
      &lt;div class='product-youtube'&gt;
          &lt;h2&gt;Video&lt;/h2&gt;
          &lt;iframe width="560" height="315" src="https://www.youtube.com/embed/xF9yc5QtNzc?feature=oembed" frameborder="0" allowfullscreen&gt;&lt;/iframe&gt;
      &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p><strong>CSS</strong></p>
  
  <pre><code>.product-page .product-spec-wrapper {
      width: 314px;
      height: 50px;
      position: relative;
      z-index: 999;
      padding-bottom: 18px;
      border-bottom: 1px solid #d9d9d9;
      padding-top: 20px;
  }
  .product-page .product-spec-wrapper .product-spec-holder {
      position: absolute;
      padding: 20px;
      right: 0px;
      top: 69px;
      display: none;
  }
  .product-page .product-spec-wrapper .product-spec-holder .additional-information-inner {
      position: relative;
      background: none #f5fee7;
  }
  .product-spec-wrapper .additional-information-inner .onajwrap {
      width: 920px;
      height: 350px;
      overflow-y: auto;
      padding-left: 2px;
      padding-right: 18px;
  }
  .clicker {
      display: none;
      position: fixed;
      z-index: 998;
      width: 5000em;
      height: 5000em;
      background-image: url("images/transparentspot.png");
      left: 0px;
      top: 0px;
  }
  .clicker.active {
      display: block;
  }
  .product-page .entry-content {
      float: left;
      width: 613px;
  }
  .product-youtube {
      width: 613px;
      margin: 20px 0 20px 0;
  }
  .product-youtube iframe {
      position:relative;
  }
  </code></pre>