A solution for subitems and also for parents is possible without JavaScript, when you will add some inline element, which will trigger hover state.
li>span:hover {
background-color: lightgray;
font-weight: bold;
}
<ul>
<li><span>fnord</span>
<ul>
<li><span>baz</span></li>
<li><span>foo</span>
<ul>
<li><span>baz</span></li>
<li><span>foo</span></li>
</ul>
</li>
</ul>
</li>
</ul>
JSFiddle here.