如何在html文档的中间重置css ?

I wonder if there are any possibility to reset css in middle of page? I have main style, but in one area I would like to use style from tinyMCE generated source. So in tinyMCE source are elements which in editor looks like default browsers style (or like user wants), but in other pages uses style from my main css and from it self inline style. So I get mix of both ant it looks crappy. And I have no idea how to reset main style,.. without iframes. I wonder if there are any possibility to reset