This is my approach, it works in my NST.
Code:
<p>(honeycomb-structure)<sup><a class="Hyperlink" href="#id04a" id="id04">[4]</a></sup></p>
<hr />
<p class="FootnoteText"><a class="Hyperlink" href="#id04" id="id04a">[4]</a> Vivienne Shue,The Reach of the state:sketches of the Chinese body politic,Stanford University Press,1998.</p>
CSS
here is the sample.
untitled sample.epub
if you use
iBooks, you can try this way , it supports pop-up footnotes and only supports by EPUB 3.0 readers.
http://www.pigsgourdsandwikis.com/20...pub-3-and.html