You can't actually turn off CSS. What you want to do is to create additional CSS that is to be applied to the part of the page where you don't want the existing definitions to apply using class names that you can attach around the part of the page where you want the new definitions to apply.
The bit I don't want to be changed by the CSS is actually remotely hosted free content from bravenet. I have already formatted this on their website, but the CSS has overridden this. Would I still have to create a separate class?