title: Popover overlay in OpenLayers 3 does not extend beyond view
body: <p>In the OpenLayers overlay example:</p>
  
  <p><a href="http://openlayers.org/en/v3.11.2/examples/overlay.html" rel="nofollow noreferrer">http://openlayers.org/en/v3.11.2/examples/overlay.html</a></p>
  
  <p>If you click near the top of map most of the overlay is hidden.  Is there a CSS trick, or an OpenLayers setting (I do not want to use the autoPan, which doesn't seem to work for popovers anyway), that will enable the entire popover to be shown even if it extends beyond the map view?</p>
  
  <p>Here's a screenshot that illustrates the problem.</p>
  
  <p><a href="https://i.stack.imgur.com/ctlfq.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ctlfq.png" alt="enter image description here"></a></p>