Change header font in category with sub category

I have changed the font size succesfully in 2 of the 3 categories we have so far. Both of the successful ones are categories with product (no subcategory).

The 3rd one has small font, and will change to the larger size (the same as cats 1 & 2) if I move the subcategory out of it.

How can I change the font to be the same size as the others?

I'm sorry - VERY new at this...I know that I copied the template in, and made changes incorrectly, but at this point, I'm stuck with it till I have a better grasp on the coding.

This is the page with the too-small-font header:

http://orphanespresso.com/index.php?main_page=index&cPath=6

The words "Gaskets & Seals" in the center box below the bread crumbs should be larger.

Thank you for any help!

Apply styling to

h1#indexCategoriesHeading {}

Thank you SO much!

I inserted:

h1#indexCategoriesHeading {
font-size: 2em
}

And now, EVERYTHING matches - YAY!