Hmm, looks like you can't unset CSS styles. Damn. This causes trouble for microformats, as it results in issues like hReview description areas being invisible in Wordpress with the default style.
I guess the solution is for blogging tools and aggregators to not use CSS classes like 'description' and 'item' (Bloglines has this problem - it makes my reviews look weird). That doesn't help much right now though. I'm thinking of putting a hack into the Structured Blogging plugin that rewrites <div class="description"> to <div class="description" style="font-size: 1em; text-align: left; color: black">, but then that would cause trouble for people not using Kubrick. Grr...
Update: I bring you: an ugly (Wordpress-specific) hack to let you give something a CSS 'description' class without making it obey the CSS 'description' rules! Here we go:
Update: The Wordpress bug report raised by ryansking (see second link from the top of this post) has been closed as 'wontfix', with a suggestion to add a CSS rule like