asp.net - check if css class exists in the stylesheet file in code behind -

I control the styles for a set of pages in the common utility method. To see what I would like to do . The CSS file is checked whether the CSS class exists or not; If this happens, choose the default.

Say both PageA.aspx and PageB.aspx use styles.css .default {...} If I wanted to have PageA.aspx styled in a different way, I could just style. I will add another entry in css .PageA {....} etc. At runtime, it will search for a CSS class called Webb, because it did not get it, it will default to the default class.

The question is how can I find out the CSS file that a special CSS class exists behind the code?

Thanks

The simplest way to apply the default style, and then page A style The browser should ignore page A declaration, if it does not exist.
I think the right thing and business; It must be used in ASP or using different files as suggested by CAB.