Remove the text from Category circles

Hi there,

I’m looking to remove the default “Category” title from the Category circle. I’ve tried looking myself, but can only seem to remove the menu title that links to the page, but not the word “Category” itself.

I’ve also tried changing the circle to an image instead, but have had no luck, as I end up with only about half of the circle changing the the image I want – this is no biggy, but if someone knew how that’d be great.

I’m very new to CSS, so sorry if this question has been asked before.
Thanks for any help!