Category font size

when I view an archive of my posts, below they all say

“posted in” category and “Leave a reply”

Ive figured out how to delete the “Leave a reply part” but not I want to change the size of the font of the category name.

I found where to do that in style.css but it changes the author of the post size and category title all at once.

I want the author title to be big and the category title to be small.

help!