simple_format helper for converting newlines to <br> css stops working

When I use the simple_format helper the css styling stops working How do I use the helper and preserve styling?

http://www.catb.org/esr/faqs/smart-questions.html

then i’ll rephrase it and post it again, please don’t answer next time

then i'll rephrase it and post it again, please don't answer next time

OK, we won't. Though I am not sure there is much point asking the
question in that case.

Colin