If this is of course a useful feature, the popup is really too big. The scrollbar that appears when the height limit is reached may be a problem: all the text should be visible without any further action from the reader. Maybe the font size should be a little smaller and so should the padding. Perhaps the shape of a flattened rectangle is more appropriate and discreet.
One last remark: the popup should appear either on click or on hover. So there are just a few details to change in my opinion and that would be perfect.