title: Changing rgba values using JavaScript and querySelector
body: <p>Lets say I have a CSS class: </p>
  
  <pre><code>.overlay {
    background-color: rgba(0,0,0,0);
  }
  </code></pre>
  
  <p>I want to change the rgba value to (0, 0, 0, 0.2)</p>
  
  <p>I want to do this WITHOUT jQuery, and I want to use the querySelector in JavaScript.</p>
  
  <p>So, if I have </p>
  
  <pre><code>var overlay = document.querySelector('.overlay');
  </code></pre>
  
  <p>How do I use this to change the background-color value?</p>
  
  <p>I've tried:</p>
  
  <pre><code>overlay.background = '(0, 0, 0, 0.2)';
  </code></pre>
  
  <p>and </p>
  
  <pre><code>overlay.backgroundColor = '(0, 0, 0, 0.2)';
  </code></pre>