Confused about paragraph width in posts and comments

Solved thanks to @MrGrey in the comments! Leaving the post text here for posterity.

Whenever I join a new site one of the first things I do is customize the style to my liking with CSS skins. I'm having a little trouble here, though, specifically with the fact that no matter what I do, I can't increase the width of the paragraphs in posts and comments.

As far as I can tell, the div.topic-text-full element spans all the way across the main element, with just a little margin space. .topic-text-full's child p elements only span maybe 80% of .topic-text-full's width, though, and my attempts to make them wider have met with failure:

.topic-full-text p {
  width: 10%;
  }

successfully shrinks the element, and so do any other widths under 100%. Setting it to any number above 100% makes no changes. Similarly, setting the width in pixels can shrink the element width, but not increase it.

The same goes if you replace .topic-full-text with .comment-text.

Is there something very simple that I'm missing? It just really bugs me that the paragraphs don't go all the way across, but since that's such a small issue I'd rather fix it on my end rather than file an official complaint about it.