template-lib/app/lib/rollup.config.js

import typescript from '@rollup/plugin-typescript';
import resolve from '@rollup/plugin-node-resolve';
import commonjs from '@rollup/plugin-commonjs';
import postcss from 'rollup-plugin-postcss';
import peerDepsExternal from 'rollup-plugin-peer-deps-external';

export default {
    input: 'src/index.ts',
    output: [
        { file: 'dist/index.cjs.js', format: 'cjs', sourcemap: true },
        { file: 'dist/index.esm.js', format: 'esm', sourcemap: true }
    ],
    plugins: [
        peerDepsExternal(),
        resolve(),
        commonjs(),
        typescript({ tsconfig: './tsconfig.json' }),
        postcss({
            modules: true,          // keep using CSS modules
            extract: 'index.css',   // <-- emit dist/index.css
            extensions: ['.css']
        })
    ],
    external: ['react', 'react-dom']
};