Managing custom styles for the RSS widget via a plugin?

I help maintain a website that uses the RSS widget to display a feed of status updates. We manage site layout using Elementor, and we apply a chunk of custom CSS to the RSS widget in order to make it fit in with the rest of the website.

This works, but it’s not very manageable: we can’t version control the changes, and if we’re working on a staging site, getting things synced back to the production site is difficult if there have been significant changes to the production site since we split off the staging copy.

Is there a way to provide custom CSS for the feed widget via a plugin? We’re already doing that to modify the cache timeout (by setting wp_feed_cache_transient_lifetime); it would be great if there were a similar mechanism available for us to provide custom styles.