Text Underline

By virtue of my simple questions, you will know I have next to no knowledge of HTML. So, I did donate! 😉

I would like to underline the post titles on my page where I have pulled one category.

I was able to figure it out in my theme, Graphene; but, it did not translate to the plug-in.

Appreciate the assistance!

http://ww.wp.xz.cn/plugins/bns-featured-category/