Create-react-app: How to use PostCSS features?

[a-x-]

Should I specify build-css and watch-css for using PostCSS nesting?
Can you help with watch-css field for PostCSS?

[gaearon]

There is no support for any PostCSS features out of the box. We are only using it for Autoprefixer internally. If you eject, you can customize the configuration, and change it to your liking.

[mihhail-lapushkin]

I've created a simple wrapper around react-scripts that injects postcss plugins to webpack config. Works like a charm for me.
Use at your own risk :)

https://github.com/mihhail-lapushkin/react-scripts-x