Rails Webpacker 3.0 import CSS file is not working

I am working Rails5 project with Webpacker in order to run React properly

But when import my css file inside my root component seems it is not working at all. Looking like stylesheet is not coming at all.

This is my root Component

import React from 'react'
import ReactDOM from 'react-dom'
import StartForm from './insurance_form/start_form'
//import PropTypes from 'prop-types'

import 'react-datepicker/dist/react-datepicker.css';
// not working

ReactDOM.render(
  <StartForm />,
  document.getElementById('start-form-index-container')
)

This my webpack/environment.js

const { environment } = require('@rails/webpacker')

const merge = require('webpack-merge')
const myCssLoaderOptions = {
    modules: true,
    sourceMap: true,
    localIdentName: '[name]__[local]___[hash:base64:5]'
}

const CSSLoader = environment.loaders.get('style').use.find(el => el.loader === 'css-loader')

CSSLoader.options = merge(CSSLoader.options, myCssLoaderOptions)

module.exports = environment

So how i can make imported css working well with webpacker?

Thanks!