How do you make Active Nav Days bolder?

On the widget, the days with active events can be clicked, but they don’t appear bold, so no one knows there are events on those days. How do you make those days bold? It seems as though the CSS class is “nav-days” and “active”, but I can’t figure out how to change their appearance.

Thanks for your help.

cidining.com/wordpress/news/

https://www.ads-software.com/plugins/events-maker/