Changing letter spacing on post view only

[Envy]

I have multiple themes on my forums, but one darker one in particular is really hard to read on the post view when there are lots of paragraphs. The front page of the forum is fine, and selecting posts is fine, but the actual topic view, when you're reading through the replies, can get really hard on the eyes.

How do I change it to be say, letter-spacing 0.5pt for the topic view only? And only for this theme? I tried via the .CSS but when I added "letter-spacing 0.5pt" anywhere, it changed the letter spacing over the whole forum, I only want it to affect the topic view...

(I didn't like it on the index page as it made everything wrap around, thus making my forum look bigger... >< )