The test file you sent doesn't appear to work, try the following taken from this tutorial:
CSS Dropdowns | HTML Dog[
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<li>
<a href="">Mammals</a>
<ul>
<li>
<a href="">Monotremes</a>
<ul>
<li><a href="">Echidnas</a></li>
<li><a href="">Platypus</a></li>
</ul>
</li>
<li>
<a href="">Marsupials</a>
<ul>
<li><a href="">Opossums</a></li>
<li><a href="">Numbats, etc.</a></li>
<li><a href="">Bandicoots, etc.</a></li>
<li><a href="">Kangaroos, koalas, wombats, etc.</a></li>
</ul>
</li>
<li>
<a href="">Placentals</a>
<ul>
<li><a href="">Primates, ungulates, etc.</a></li>
<li><a href="">Anteaters, sloths, etc.</a></li>
<li><a href="">Elephants, etc.</a></li>
</ul>
</li>
</ul>
</li>