Webpack loader fails when importing .css in react_on_rails app?

I am trying to use react-datetime on my react-on-rails app. To make the datetime work out of the box, I need to import the CSS mentioned on their GH page.

On my app, I copy/paste the CSS into a file I named DateTime.css:

...
import DateTime from 'react-datetime';
import '../../schedules/stylesheets/DateTime.css';
...

export default class AddDate extends React.Component {

But it gives me this error:

VM45976:1 Uncaught Error: Module parse failed: /Users/some/path/to/my/project/App/components/schedules/stylesheets/DateTime.css Unexpected token (1:0)
You may need an appropriate loader to handle this file type.
| .rdt {
|   position: relative;
| }

It seems like the CSS loader is not working. I tried this on pure react app (create-react-app) and it worked. It broke when I did it inside react_on_rails.

This is my webpack config atm (standard out-of-the-box react_on_rails):

const webpack = require('webpack');
const { resolve } = require('path');

const ManifestPlugin = require('webpack-manifest-plugin');
const webpackConfigLoader = require('react-on-rails/webpackConfigLoader');

const configPath = resolve('..', 'config');
const { devBuild, manifest, webpackOutputPath, webpackPublicOutputDir } =
  webpackConfigLoader(configPath);

const config = {

  context: resolve(__dirname),

  entry: {
    'webpack-bundle': [
      'es5-shim/es5-shim',
      'es5-shim/es5-sham',
      'babel-polyfill',
      './app/bundles/App/startup/registration',
    ],
  },

  output: {
    // Name comes from the entry section.
    filename: '[name]-[hash].js',

    // Leading slash is necessary
    publicPath: `/${webpackPublicOutputDir}`,
    path: webpackOutputPath,
  },

  resolve: {
    extensions: ['.js', '.jsx'],
  },

  plugins: [
    new webpack.EnvironmentPlugin({
      NODE_ENV: 'development', // use 'development' unless process.env.NODE_ENV is defined
      DEBUG: false,
    }),
    new ManifestPlugin({ fileName: manifest, writeToFileEmit: true }),
  ],

  module: {
    rules: [
      {
        test: require.resolve('react'),
        use: {
          loader: 'imports-loader',
          options: {
            shim: 'es5-shim/es5-shim',
            sham: 'es5-shim/es5-sham',
          },
        },
      },


    {
        test: /\.jsx?$/,
        use: 'babel-loader',
        exclude: /node_modules/,
      },
      {
        test: /\.css$/,
        use: 'css-loader',
        exclude: /node_modules/,
      },
    ],
        ],
      },
    };

module.exports = config;

if (devBuild) {
  console.log('Webpack dev build for Rails'); // eslint-disable-line no-console
  module.exports.devtool = 'eval-source-map';
} else {
  console.log('Webpack production build for Rails'); // eslint-disable-line no-console
}

I am very new in webpack, and not sure how to I can add loaders to make it work, how can I apply the DateTime.css file that I have to be applied to react-datetime?

EDIT: added css-loader (also updated the webpack above). It is no longer complaining that I don't have the correct loader, but the CSS does not work.

{
    test: /\.jsx?$/,
    use: 'babel-loader',
    exclude: /node_modules/,
  },
  {
    test: /\.css$/,
    use: 'css-loader',
    exclude: /node_modules/,
  },
],

Solution

There are 2 conceptually different ways to approach this.

1. Using CSS modules. This way your CSS will end up bundled with your JS and as soon as webpack loads that JS module/bundle it will automatically append CSS style element into the head. In my project I have this rule to do exactly that (note that we use both css-loader and style-loader):

{
    test: /\.css$/,
    use: ['style-loader', {
        loader: 'css-loader',
        options: {
            modules: true,
            localIdentName: '[path][name]__[local]--[hash:base64:5]'
        }
    }]
}

More on css-loader modules at this link.

2. Using ExtractTextPlugin. This way all your CSS will be extracted into a separate file. The configuration requires 2 things: a plugin and loaders configuration created by the plugin:

const ExtractTextPlugin = require('extract-text-webpack-plugin');
// Add this to your webpack plugins array
new ExtractTextPlugin('styles.css')

And add this to your rules:

{
    test: /\.css$/,
    exclude: /node_modules/,
    use: ExtractTextPlugin.extract({
        fallback: 'style-loader',
        use: ['css-loader']
    })
}

This will create one single styles.css file and put all CSS you import from JS into that file.