Formatting product category descriptions

Hi again,

I was hoping someone could help me with this question.
I have gridmarket running on a marketpress.I want to format the product category descriptions. As it is now my product category name is large at 45px but I want to make the associated category description smaller at around 24px. I have figured out how to change format on the product post title with h1.post-title but I am unsure how to change the .css on the post description
To clarify this is not the individual product description but the category description found as follows
dashboard>products>product categories>editing individual categories>product category description.

Many Thanks
Meriam