Styling subpage widget

Hello
I m new to Wordpress and this theme so aapologies in advance if I missed something obvious.
I m trying build a subpage navigation menu. I created a new widget field in the center and I installed the Subpages plugin. This all works but now I want to style the links to the subpages differently. I want them to be horizontally oriented and a different font, linkhover color, size etc. Where can I do that?

www.vnugrda.net/Rieskrater is the page I m working on.
thanks