[KevinH]

It works as designed. You used no pre-wrap (pre) tag. Prettify assumes you want to actually change xhtml whitespace to prettify the layout. Prettifying has no idea about your css, it is run on xhtml source. If you want to preserve your pre-wrapped code, through the prettifying process you need to use the pre and code xhtml tags and not assume css is doing anything here as css can and does change independently of your xhtml. It was designed to do that.

So either use pre/code tags in your xhtml source before running Prettify or don't choose to Prettify the xhtml code.