O_o Looking at your code it seems to me your font size is currently set to 10em instead of the default 1em. Could it possible that you set it to 10px and that because a recent patch switched the unit to em for better accessibility, it kept the 10 but switched px to em? Have you checked at http://www.dreamwidth.org/customize/options?

Edit: Looks like we posted at the same time. Glad you figured it out. :)