Opening in React devtools shows a number of hints[1]. "React Native Style Editor" section. "View" components with numeric "style" props. And the classname prefixes "css-" and "r-" match the generated identifiers from react-native-web[2].

[1]: https://imgur.com/lFUvL7P

[2]: https://github.com/necolas/react-native-web/blob/45f94eb43da...