title: Change webkit-scrollbar-track-piece's color when webkit-scrollbar-thumb is hovered?
body: <p>I have the following CSS rule:</p>
  
  <pre><code>::-webkit-scrollbar-thumb:vertical:hover {
      background-color: #666;
  }
  </code></pre>
  
  <p>I want to also decorate webkit-scrollbar-track-piece when webkit-scrollbar-thumb is hovered. Something like:</p>
  
  <pre><code>//  Doesn't work:
  ::-webkit-scrollbar-thumb:vertical:hover ::-webkit-scrollbar-track-piece {
      background-color: red !important;
  }
  </code></pre>
  
  <p>Is this possible with just CSS using another expression that I'm not aware of? Or is this not possible to do currently?</p>