title: How to make top bar go transparent when scrolling down?
body: <p>Right now i have one bar located on top and here is the <code>CSS</code> for it:</p>
  
  <pre><code>#header_bar { 
    background: #000000;
    height: 60px;
    position: fixed;
    top: 0px;
    width: 100%;
    z-index: 10020;
  }
  </code></pre>
  
  <p>My question is, how i can make this bar go transparent when the page is scrolled?</p>
  
  <p>Should i use opacity option somehow?</p>
  
  <p>Thanks in advance!</p>