css-loader not importing .css file returning empty object

You can fix your problem with three ways :

#1: Replace 'css-loader' with 'css-loader?modules=true&camelCase=true'

#2: Do old school like this :

##index.js

import React from 'react'   
import './header.css'

export default class Header extends React.PureComponent {
  render() {
    return(
      <header className="header">
        This is header component
      </header>
    )
  }
}

#3: use babel-plugin-react-css-modules or React CSS Modules

I wonder if this is perhaps you are not using css-modules. The example you are showing there is an example of implementing the css-modules feature of the loader.

Perhaps try adding the ?modules query to your css-loader definition.