What formatting does ibooks support in an aside element?

I am compiling an epub for reading in ibooks and on the iphone. The book has numerous footnotes that I plan to display via the aside element, since iBooks supports a popup style for footnotes in the aside element. The problem is that no formatting from the css file appears in the aside element. The only formatting I can make appear is via a <span class="font-style:italic"> content </span> type construct in the aside. Has anyone found any way for the aside to recognize and take advantage of the formatting in a css file?

I am using iBooks version 1.1.1 (600) and writing the files with TextWrangler, not iBooks Author. But I assume the same dilemma would be faced by someone using iBooks Author. Thanks in advance.