The structure of a definition list should be something like:
<dl>
<dt>Some title</dt>
<dd>Your definition</dd>
</dl>
Do you have anything other than text in the <dd> that might have styles being applied to them that override your dl dd CSS, like a <span> or <strong> or <em>?
EDIT:
Saw your update. It definitely DOES have to do with your <pre> tags. Your CSS rules don't override the <pre> because that sort of defeats the purpose of "pre-formatted text."
Try expanding your CSS to include <pre> in the chain of selectors, and use !important:
dl dd pre {
font-size: 12px;
font-weight: bold !important;
}
See if that works and report back.