rollup.config.js

import svelte from 'rollup-plugin-svelte';
import resolve from '@rollup/plugin-node-resolve';
import commonjs from '@rollup/plugin-commonjs';
import livereload from 'rollup-plugin-livereload';
import { terser } from 'rollup-plugin-terser';
import sveltePreprocess from 'svelte-preprocess';
import typescript from '@rollup/plugin-typescript';
import smelte from 'smelte/rollup-plugin-smelte';

const production = !process.env.ROLLUP_WATCH;

export default {
	input: 'src/main.ts',
	output: {
		sourcemap: true,
		format: 'iife',
		name: 'app',
		file: 'public/build/bundle.js'
	},
	plugins: [
		svelte({
			// enable run-time checks when not in production
			dev: !production,
			// we'll extract any component CSS out into
			// a separate file - better for performance
			css: css => {
				css.write('public/build/bundle.css');
			},
			emitCss: true, // this is neccessary for emitted by svelte styles to be included in the build, otherwise postcss will overwrite them
			preprocess: sveltePreprocess(),
		}),

		// If you have external dependencies installed from
		// npm, you'll most likely need these plugins. In
		// some cases you'll need additional configuration -
		// consult the documentation for details:
		// https://github.com/rollup/plugins/tree/master/packages/commonjs
		resolve({
			browser: true,
			dedupe: ['svelte']
		}),
		commonjs(),
		smelte({ 
			purge: production,
			output: "public/build/global.css", // it defaults to static/global.css which is probably what you expect in Sapper 
			postcss: [], // Your PostCSS plugins
			whitelist: [], // Array of classnames whitelisted from purging
			whitelistPatterns: [], // Same as above, but list of regexes
			tailwind: { 
				colors: { 
					primary: "#1e3f5a",
					secondary: "#009688",
					error: "#f44336",
					success: "#4caf50",
					alert: "#ff9800",
					blue: "#2196f3",
					dark: "#212121" 
				}, // Object of colors to generate a palette from, and then all the utility classes
				darkMode: true, 
			}, 
			// Any other props will be applied on top of default Smelte tailwind.config.js
		}),
		typescript({ sourceMap: !production }),

		// In dev mode, call `npm run start` once
		// the bundle has been generated
		!production && serve(),

		// Watch the `public` directory and refresh the
		// browser on changes when not in production
		!production && livereload('public'),

		// If we're building for production (npm run build
		// instead of npm run dev), minify
		production && terser()
	],
	watch: {
		clearScreen: false
	}
};

function serve() {
	let started = false;

	return {
		writeBundle() {
			if (!started) {
				started = true;

				require('child_process').spawn('npm', ['run', 'start', '--', '--dev'], {
					stdio: ['ignore', 'inherit', 'inherit'],
					shell: true
				});
			}
		}
	};
}