Ant Design offers the most components with JS and CSS taken care of. They look clean, professional, and usable.
We paired this with Bulma for making the containers and structure reactive. Bulma (for react) make it easy to just add a section, container, and content and have it work on all platforms.
We also use Geist UI, though not recognized by Stack share, for its simple and modern feel. Highly recommend Geist if you want modern components for complicated UI's