Repository: storybook
Issue: Styles not getting applied in storybook v6 - using postcss/css modules
Labels: question / support,react

**Describe the bug**
Every time I run storybook none of the styles/classes are not getting applied to the components. The component stories are generated ok just with no styles. 

But when I add the components into an app it all works fine.

**To Reproduce**
Running the command `start-storybook -c .storybook -p 6006` from the root

**Expected behavior**
Styles to be applied to the components in storybook

**Code snippets**
Button.component.tsx
```
import React from 'react';
import cx from 'classnames';

import * as styles from './button.module.css';

export interface IButtonProps
  extends React.ButtonHTMLAttributes<HTMLButtonElement> {
  /**
   * Sets chosen styling of the button
   */
  buttonStyle: 'primary' | 'secondary' | 'tertiary';
  /**
   * Checks if the button should be full width
   */
  isFullWidth?: boolean;
  /**
   * Sets the type of button to render
   */
  type: 'button' | 'submit' | 'reset';
}

/**
 * Primary UI component for user interaction
 */
export const Button: React.FC<IButtonProps> = ({
  children,
  buttonStyle,
  isFullWidth,
  type,
  ...props
}) => (
  <button
    className={cx(styles.button, {
      [styles[buttonStyle]]: buttonStyle,
      [styles.fullWidth]: isFullWidth,
    })}
    data-testid={buttonStyle}
    {...props}
  >
    {children}
  </button>
);

Button.defaultProps = {
  buttonStyle: 'primary',
  isFullWidth: false,
  type: 'button',
};
```
Button.module.css
```
.button {
  align-items: center;
  background: transparent;
  border: 0;
  border-radius: 8px;
  cursor: pointer;
  display: inline-flex;
  font-family: Barlow, sans-serif;
  font-kerning: none;
  font-size: 16px;
  font-weight: 700;
  justify-content: center;
  line-height: 1.5;
  outline: none;
  padding: 12px 16px;
  position: relative;
  transition: all 200ms ease-in-out;
  white-space: nowrap;
  width: auto;

  &[disabled] {
    cursor: not-allowed;
  }
}

.primary {
  background-color: #e10a0a;
  border: 1px solid transparent;
  color: #fff;

  &:hover {
    background-color: #fff;
    border: 1px solid #e10a0a;
    color: #e10a0a;
  }
}

.secondary {
  background-color: #fff;
  border: 1px solid #e3e3e3;
  color: #e10a0a;

  &:hover {
    border: 1px solid #e10a0a;
  }
}

.fullWidth {
  width: 100%;
}
```
.storybook/main.js
```
module.exports = {
  stories: ['../packages/components/**/**/*.stories.@(tsx|ts)'],
  addons: ['@storybook/addon-essentials', '@storybook/addon-a11y'],
  webpackFinal: async (config, { configType }) => {
    // `configType` has a value of 'DEVELOPMENT' or 'PRODUCTION'
    // You can change the configuration based on that.
    // 'PRODUCTION' is used when building the static version of storybook.

    // Make whatever fine-grained changes you need
    config.module.rules.push({
      test: /\.css$/,
      use: [{
        loader: 'css-loader',
        options: {
          modules: true
        }
      }, 'postcss-loader'],
      include: path.resolve(__dirname, '../'),
    });

    // Return the altered config
    return config;
  },
};
```

**System**
Environment Info:

  System:
    OS: macOS 10.15.7
    CPU: (16) x64 Intel(R) Core(TM) i9-9980HK CPU @ 2.40GHz
  Binaries:
    Node: 12.18.3 - ~/.nvm/versions/node/v12.18.3/bin/node
    Yarn: 1.22.5 - ~/.yvm/shim/yarn
    npm: 6.14.6 - ~/.nvm/versions/node/v12.18.3/bin/npm
  Browsers:
    Chrome: 87.0.4280.67
    Edge: 87.0.664.52
    Firefox: 81.0
    Safari: 14.0.1
  npmPackages:
    @storybook/addon-a11y: ^6.1.9 => 6.1.9 
    @storybook/addon-essentials: ^6.1.9 => 6.1.9 
    @storybook/addon-info: ^5.3.21 => 5.3.21 
    @storybook/addon-viewport: ^6.1.9 => 6.1.9 
    @storybook/addons: ^6.1.9 => 6.1.9 
    @storybook/preset-typescript: ^3.0.0 => 3.0.0 
    @storybook/react: ^6.1.9 => 6.1.9 
    @storybook/theming: ^6.1.9 => 6.1.9 


**Additional context**
Add any other context about the problem here.