PRObeaver is a website specialising in Beaver Builder tutorials and resources and they publish a number of CSS stylesheets for the Beaver Builder Tabs and Accordion modules.
The site is run by Davinder Singh Kainth who specialises in Beaver Builder and Genesis Child Theme development. PRObeaver has published a really useful Beaver Builder hooks guide on their site. Check it out here.
Davinder also publishes a weekly Beaver Builder update; subscribe here.