title: How to add height to existing height?
body: <p>For example I want to add <code>20px</code> to <code>&lt;div id='example'&gt;&lt;/div&gt;</code>, which is currently <code>20px</code>. </p>
  
  <p>I could get the existing height and add <code>20px</code> and input it as the new height, but I wish to learn if there is a better way that might work like a <code>+=</code> operator. </p>