CSS Selectable Pages

Consider the following scenario. We have a portal with decades or hundreds of pages. Some of those pages include content that needs special styles to look good. Inline CSS is not an option as we talk about a good amount of CSS code. What we need is CSS selectors that will target on those specific pages. How can we do that?
Introducing CSS Selectable Pages
I always wrap my skin code in a DIV. It helps me in several ways, like avoiding CSS conflicts or writing styles for a page skin without having to create an additional CSS file.
That usually goes like this: