Change Appearance of On Page Feed

I’m using the feed with excerpts on a page (this one is an example: https://savorlife.com/WordPress/the-grapevine/) but I’d love to change the appearance a little bit. Like, maybe a border around each episode or something to make each episode stand apart from one another?

Is there a settings section somewhere that I’m just not finding? Or, is this typically done with custom CSS?