Does it not work to use a declaration like:
a.topiclinks { display: block; }
IOW, what's called a class selector (the . dot and the class name)? Regardless of how it actually gets to work, you need to pay most attention to [link|http://www.w3.org/TR/REC-CSS2/selector.html#child-selectors|chapter 5 in the CSS2 spec], which covers selectors. This was one of the harder things for me to get into my head, but made all the difference. Almost everything else is just learning syntax; chap 5 is the conceptual biggie.