title: CSS module is not working in react 16.13.1
body: <p>I want to style components in react JS. I tried several ways to do that. When I try to create a CSS object and apply it to the component in the same JS file, then it is working. But when I try to apply CSS from external CSS file and import it in the JS file then it is not working. And I have also tried to save that file as <code>filename.module.css</code>. But it didn't help me.</p>
  
  <p>The list of installed node modules and their versions is given below.</p>
  
  <pre><code>&gt; @material-ui/core@4.9.11
  &gt; @material-ui/icons@4.9.1
  &gt; firebase@7.14.1
  &gt; react@16.13.1
  &gt; react-dom@16.13.1
  &gt; react-router-dom@5.1.2
  &gt; react-scripts@3.4.1
  </code></pre>
  
  <p>In <code>webpack.config.js</code> file of <code>react-script</code> module, I found below code:</p>
  
  <pre><code>const cssRegex = /\.css$/;
  const cssModuleRegex = /\.module\.css$/;
  const sassRegex = /\.(scss|sass)$/;
  const sassModuleRegex = /\.module\.(scss|sass)$/;
  </code></pre>
  
  <p>So I guess my react project is supporting CSS files as well as SCSS and SASS files. Did I understand correctly?</p>
  
  <p><code>header.module.css</code> file:</p>
  
  <pre><code>.heading {
      color: '#3592EF';
      font-weight: '600';
      letter-spacing: '2px';
  }
  .navButton {
      color: '#444';
      font-size: '16px';
      padding: '4px 8px';
      margin: 'auto';
      margin-right: '15px';
  }
  </code></pre>
  
  <p><code>Header.js</code> file:</p>
  
  <pre><code>import React from 'react';
  import { Button } from '@material-ui/core';
  import styles from './header.module.css';
  
  export default class Header extends React.Component {
      render() {
          return (
              &lt;div&gt;
                  &lt;span className={styles.headling}&gt;Heading element&lt;/span&gt;
                  &lt;Button className={styles.navButton}&gt;Home&lt;/Button&gt;
                  &lt;Button className={styles.navButton}&gt;About&lt;/Button&gt;
              &lt;/div&gt;
          );
      }
  }
  </code></pre>
  
  <p>The output is coming with the Heading element and Home, About button. But without CSS style.</p>
  
  <p>How can I solve this issue?</p>
  
  <p>Thank you.</p>