css – WordPress sidebar code edits

I need to edit the title of a sidebar widget on my site, I need to change the color and make it bold also preferably. How do I go about doing this? I’m guessing it invlolves editing CSS code and I haven’t been able to edit the stylesheet and get it to work. Any ideas? The site is using this theme – https://klbtheme.com/bacola/shop/. Eg. I need to change the product categories title size and color in this case.

Any help would be much appreciated. Thanks in advance!