title: Changing background color opacity on mouseover
body: <p>I have a DIV that I'd like to change the background color opacity on, depending on if the mouse is over it or not.</p>
  
  <p>I know you can use <code>background: rgba(54, 25, 25, .5)</code> etc, but I want to set the colour separately. Is there any way I can JUST modify the OPACITY, and not the colour.</p>
  
  <p>I could <code>opacity: 0.3</code>, etc, but that effects the whole DIV, and I just want to affect the background colour.</p>