git clone https://gist.github.com/b3db0d9bd810626bf3acf7329f3bcccd.git foo && cd foo && npm i && npm start

.gitignore

node_modules
npm-debug.log
dist
build

index.js

// import 'material-design-icons';
import { Component } from 'preact';
import DatePicker from 'react-toolbox/lib/date_picker';

export default class App extends Component {
	state = {
		date: new Date()
	};

	updateDate = date => {
		this.setState({ date });
	};

	render({ }, { date }) {
		return (
			<div>
				<link href="https://fonts.googleapis.com/icon?family=Material+Icons" rel="stylesheet" />
				<h1>Date Picker Example</h1>
				<DatePicker
					label="PickaDate"
					value={date}
					onChange={this.updateDate}
				/>
			</div>
		);
	}
}

package.json

{
  "name": "date-picker-demo",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "eslint src && preact test",
    "start": "if-env NODE_ENV=production && npm run -s serve || npm run -s dev",
    "build": "preact build",
    "serve": "preact build && preact serve",
    "dev": "preact watch"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "eslintConfig": {
    "extends": "eslint-config-synacor"
  },
  "devDependencies": {
    "eslint": "^4.6.1",
    "eslint-config-synacor": "^1.1.1",
    "if-env": "^1.0.0",
    "postcss-cssnext": "^3.0.2",
    "postcss-each": "^0.10.0",
    "postcss-import": "^10.0.0",
    "postcss-mixins": "^6.1.0",
    "postcss-modules-scope": "^1.0.2",
    "preact-cli": "^1.4.1",
    "preact-cli-postcss": "^1.0.0"
  },
  "dependencies": {
    "preact": "^8.2.5",
    "preact-compat": "^3.17.0",
    "preact-router": "^2.5.7",
    "react-toolbox": "^2.0.0-beta.12"
  }
}

postcss.config.js

module.exports = {
	plugins: {
		'postcss-import': {
			root: __dirname
		},
		'postcss-mixins': {},
		'postcss-each': {},
		'postcss-cssnext': {}
	}
};

preact.config.js

import path from 'path';
import postcss from 'preact-cli-postcss';

const reactToolboxPath = path.resolve('./node_modules', 'react-toolbox');

export default (config, env, helpers) => {
	postcss(config, helpers);

	const rules = helpers.getLoadersByName(config, 'postcss-loader');
	const cssModulesRule = rules[0].rule;
	cssModulesRule.include.push(reactToolboxPath); // this enables css modules for react-toolbox
	const globalCssRule = rules[1].rule;
	globalCssRule.exclude.push(reactToolboxPath); // exclude react-toolbox from global css
};