title: Why does getPropertyValue return an empty string instead of the element's style property?
body: <p>This seems to only happen when I use "background" in the parameters of <code>getPropertyValue();</code>:</p>
  
  <pre><code>var d = document.getElementById('myDiv');
  
  window.getComputedStyle(d).getPropertyValue('background'); // ""
  </code></pre>
  
  <p>Why does it return an empty string and how can I get this to return the actual background css property?</p>