OK first of all, almost to obvious to say, but are you talking about checkboxes or radiobuttons? Not strictly relevant to your question but if you're confused about something as basic as that, I'm a little concerned.

Secondly, show us the HTML, it'll mean we don't have to render it ourselves! This isn't a Perl question at all, really...

Thirdly, having rendered it myself, I can clearly see that this:

<input type="checkbox" name="x" value="foo" class="RadioButtons" />
foo
<input type="checkbox" name="x" value="bar" class="RadioButtons" />
bar
<input type="checkbox" name="x" value="baz" class="RadioButtons" />
baz
[download]

appears, or something like it. So the classes are attached to the buttons themselves, not the text which goes next to them. So your CSS has no effect on the text. Wrap the whole thing in a DIV instead.