Two things, now that I know you're talking about the Categories sidebox links:

Zencart loads all stylesheets with the css extension that are in the current template's css folder, so you have two sheets fighting each other. Rename stylesheetlast.css (or stylesheet.css) to stylesheet.old or move it to a different folder.

Stylesheets are applied top to bottom, so your a.category-top rule is being overridden by subsequent a rule(s). Place that rule at the bottom of the sheet, and it should work.