title: aria-hidden property not working on descendants
body: <p>Chrome Accessibility Tools complains that certain children of an overlay box do not have the right contrast ratio. It seems like the tool considers the children to be "visible" when the overlay is hidden. </p>
  
  <p>I can see the <code>aria-hidden</code> property of the overlay being correctly set in the inspector as I open/close it, though (using <code>attr("aria-hidden","false");</code>).</p>
  
  <p>Setting <code>aria-hidden="true";</code> through the inspector on the children individually fixes this problem.</p>
  
  <p>I am confused as aria-hidden is supposed to hide the element <em>and</em> its children. 
  Does anyone know what I am doing wrong?</p>