title: Javascript style properties are not set
body: <p>This is my CSS-code:</p>
  
  <pre><code>div.dropdown
  {
      width: 100%;
      height: 130px;
      background-color: white;
      border: solid thin #666;
      position:absolute;
      font-size: 70px;
      padding-top: 30px;
      text-align:center;
      top: calc(100% - 320px);
  }
  </code></pre>
  
  <p>If I try to get the top-property in javascript using <code>window.getComputedStyle(dropdown).top</code>, I get an empty value.</p>
  
  <p>How can I get the top value?</p>
  
  <p>I found out that if I set the top-property to calc(100%) (just for testing), the aforementioned method works well.</p>
  
  <p>This is the javascript code:</p>
  
  <pre><code>function show_dropdown(dropdown_id, dropdown_menu_id)
  {
      var dropdown = document.getElementById(dropdown_id);
      var menu = document.getElementById(dropdown_menu_id);
      var menu_entries = Array.prototype.slice.call(menu.childNodes);
  
      var dropdown_top = parseInt(window.getComputedStyle(dropdown).top);
  
      ...  
  }
  </code></pre>