Blog Description CSS broken in Blogger?

When I try to use CSS to change the size and style of the blog description font, it simply will not allow it. Luckily, I decided to practice this on the blog I worry about least. Hmm, what could be the problem? I did it just as the directions show. Go into the CSS editor. Use the code: .description{font-size: (any number) px;}  Does not work! And the same for the font style.