title: CSS on condition
body: <p>Does CSS support conditions? I mean that there is hover, so when mouse is on it, element style changes.
  I have class <code>".menu_top_line"</code> with <code>display:none</code>, can I change it to <code>"display:block"</code>, when mouse is on other element?
  Like:</p>
  
  <pre><code>nav ul li:hover
  {
      background-color:#FFF;
      // other block.display:block
  }
  </code></pre>