title: Styling an inner scrollbar like the Twitter conversation interface?
body: <p><img src="https://i.stack.imgur.com/BdCDe.png" alt="Side panel scrollbar"></p>
  
  <p>The scroll bar can be seen in the side-panel when you click on a tweet and the conversation linked to the tweet is long enough.</p>
  
  <p><strong>How is the scroll bar created and styled?</strong></p>