React Native is not supporting the full browser CSS as we know it. It contains only a subset of browser's CSS properties for styling. Also there is no support for complex CSS selectors.
“What is the difference with regular CSS and React Native's CSS?
React Native's styling works a bit differently compared to regular CSS:
Even with the above differences, React Native's CSS implementation is still almost fully compatible with the one in Web browsers. You can think of it as a stricter subset of the CSS that is used in browsers.
The supported styling depends on the element that you want to style. You can have a look at the example apps, or this cheat sheet when writing your styles: https://github.com/vhpoet/react-native-styling-cheat-sheet
If you plan to use the same CSS files for both React Native and Web, then I suggest that you build your app "React Native first". It is much easier to build the app with React Native's styling limitations, and then make it work for web using React Native for Web.”, credits.
So yes you need to maintain 2 different stylesheets, but you can have different approaches:
Hope this helps.
It is possible to import css/sass files for use in react native styling. This should allow for some reuse of styling