RSS Feed Widget – Change font size – Additional CSS

I have a default RSS Feed Widget on the right side below the video feed section on my home page.
The font of the feed URL titles is much too big and I want to make them smaller.
How can I use the additional CSS on the block to reduce the size.
The Class ID as far as I can make out is rsswidget – but may be wrong.

I am using latest WP version with latest version Newspaper theme.

The page I need help with: [log in to see the link]