Try .linklist-item (Note the . that’s at the start of the class name. It needs to be included.)
You could also try .linklist-item .linklist-item-title, .linklist-item .linklist-item-description
You’ll need to wait up to 10 minutes to see the changes. If you have access to your Discourse site’s Rails console, you can clear the cache by running Rails.cache.clear. That way you can see the changes right away.