初学react 用的官方的creat-react-app创建的项目 我在组件里了导入footer.css样式文件没有生效，打印这个footerCss发现就是空对象 应该是样式并没有导入进来吧
不知道 是不是还需要配置一下config.dev文件
import React from 'react';
import footerCss from '../css/footer.css'

export default class Footer extends React.Component {

render() {
    console.log(footerCss)
    return (
        <footer className={footerCss.bg}>
          <h3>这是底部组件</h3>
        </footer>
    )
}

}

但是这里面应该是配置好的才对
'use strict';

const autoprefixer = require('autoprefixer');
const path = require('path');
const webpack = require('webpack');
const HtmlWebpackPlugin = require('html-webpack-plugin');
const CaseSensitivePathsPlugin = require('case-sensitive-paths-webpack-plugin');
const InterpolateHtmlPlugin = require('react-dev-utils/InterpolateHtmlPlugin');
const WatchMissingNodeModulesPlugin = require('react-dev-utils/WatchMissingNodeModulesPlugin');
const eslintFormatter = require('react-dev-utils/eslintFormatter');
const ModuleScopePlugin = require('react-dev-utils/ModuleScopePlugin');
const getClientEnvironment = require('./env');
const paths = require('./paths');

// Webpack uses publicPath to determine where the app is being served from.
// In development, we always serve from the root. This makes config easier.
const publicPath = '/';
// publicUrl is just like publicPath, but we will provide it to our app
// as %PUBLIC_URL% in index.html and process.env.PUBLIC_URL in JavaScript.
// Omit trailing slash as %PUBLIC_PATH%/xyz looks better than %PUBLIC_PATH%xyz.
const publicUrl = '';
// Get environment variables to inject into our app.
const env = getClientEnvironment(publicUrl);

// This is the development configuration.
// It is focused on developer experience and fast rebuilds.
// The production configuration is different and lives in a separate file.
module.exports = {
// You may want 'eval' instead if you prefer to see the compiled output in DevTools.
// See the discussion in https://github.com/facebookin...
devtool: 'cheap-module-source-map',
// These are the "entry points" to our application.
// This means they will be the "root" imports that are included in JS bundle.
// The first two entry points enable "hot" CSS and auto-refreshes for JS.
entry: [

// We ship a few polyfills by default:
require.resolve('./polyfills'),
// Include an alternative client for WebpackDevServer. A client's job is to
// connect to WebpackDevServer by a socket and get notified about changes.
// When you save a file, the client will either apply hot updates (in case
// of CSS changes), or refresh the page (in case of JS changes). When you
// make a syntax error, this client will display a syntax error overlay.
// Note: instead of the default WebpackDevServer client, we use a custom one
// to bring better experience for Create React App users. You can replace
// the line below with these two lines if you prefer the stock client:
// require.resolve('webpack-dev-server/client') + '?/',
// require.resolve('webpack/hot/dev-server'),
require.resolve('react-dev-utils/webpackHotDevClient'),
// Finally, this is your app's code:
paths.appIndexJs,
// We include the app code last so that if there is a runtime error during
// initialization, it doesn't blow up the WebpackDevServer client, and
// changing JS code would still trigger a refresh.

],
output: {

// Add /* filename */ comments to generated require()s in the output.
pathinfo: true,
// This does not produce a real file. It's just the virtual path that is
// served by WebpackDevServer in development. This is the JS bundle
// containing code from all our entry points, and the Webpack runtime.
filename: 'static/js/bundle.js',
// There are also additional JS chunk files if you use code splitting.
chunkFilename: 'static/js/[name].chunk.js',
// This is the URL that app is served from. We use "/" in development.
publicPath: publicPath,
// Point sourcemap entries to original disk location (format as URL on Windows)
devtoolModuleFilenameTemplate: info =>
  path.resolve(info.absoluteResourcePath).replace(/\\/g, '/'),

},
resolve: {

// This allows you to set a fallback for where Webpack should look for modules.
// We placed these paths second because we want `node_modules` to "win"
// if there are any conflicts. This matches Node resolution mechanism.
// https://github.com/facebookincubator/create-react-app/issues/253
modules: ['node_modules', paths.appNodeModules].concat(
  // It is guaranteed to exist because we tweak it in `env.js`
  process.env.NODE_PATH.split(path.delimiter).filter(Boolean)
),
// These are the reasonable defaults supported by the Node ecosystem.
// We also include JSX as a common component filename extension to support
// some tools, although we do not recommend using it, see:
// https://github.com/facebookincubator/create-react-app/issues/290
// `web` extension prefixes have been added for better support
// for React Native Web.
extensions: ['.web.js', '.mjs', '.js', '.json', '.web.jsx', '.jsx'],
alias: {
  
  // Support React Native Web
  // https://www.smashingmagazine.com/2016/08/a-glimpse-into-the-future-with-react-native-for-web/
  'react-native': 'react-native-web',
},
plugins: [
  // Prevents users from importing files from outside of src/ (or node_modules/).
  // This often causes confusion because we only process files within src/ with babel.
  // To fix this, we prevent you from importing files out of src/ -- if you'd like to,
  // please link the files into your node_modules/ and let module-resolution kick in.
  // Make sure your source files are compiled, as they will not be processed in any way.
  new ModuleScopePlugin(paths.appSrc, [paths.appPackageJson]),
],

},
module: {

strictExportPresence: true,
rules: [
  // TODO: Disable require.ensure as it's not a standard language feature.
  // We are waiting for https://github.com/facebookincubator/create-react-app/issues/2176.
  // { parser: { requireEnsure: false } },

  // First, run the linter.
  // It's important to do this before Babel processes the JS.
  {
    test: /\.(js|jsx|mjs)$/,
    enforce: 'pre',
    /*use: [
      {
        options: {
          formatter: eslintFormatter,
          eslintPath: require.resolve('eslint'),
          
        },
        loader: require.resolve('eslint-loader'),
      },
    ],*/
    include: paths.appSrc,
  },
  {
    // "oneOf" will traverse all following loaders until one will
    // match the requirements. When no loader matches it will fall
    // back to the "file" loader at the end of the loader list.
    oneOf: [
      // "url" loader works like "file" loader except that it embeds assets
      // smaller than specified limit in bytes as data URLs to avoid requests.
      // A missing `test` is equivalent to a match.
      {
        test: [/\.bmp$/, /\.gif$/, /\.jpe?g$/, /\.png$/],
        loader: require.resolve('url-loader'),
        options: {
          limit: 10000,
          name: 'static/media/[name].[hash:8].[ext]',
        },
      },
      // Process JS with Babel.
      {
        test: /\.(js|jsx|mjs)$/,
        include: paths.appSrc,
        loader: require.resolve('babel-loader'),
        options: {
          
          // This is a feature of `babel-loader` for webpack (not Babel itself).
          // It enables caching results in ./node_modules/.cache/babel-loader/
          // directory for faster rebuilds.
          cacheDirectory: true,
        },
      },
      // "postcss" loader applies autoprefixer to our CSS.
      // "css" loader resolves paths in CSS and adds assets as dependencies.
      // "style" loader turns CSS into JS modules that inject <style> tags.
      // In production, we use a plugin to extract that CSS to a file, but
      // in development "style" loader enables hot editing of CSS.
      {
        test: /\.css$/,
        use: [
          require.resolve('style-loader'),
          {
            loader: require.resolve('css-loader'),
            options: {
              importLoaders: 1,
            },
          },
          {
            loader: require.resolve('postcss-loader'),
            options: {
              // Necessary for external CSS imports to work
              // https://github.com/facebookincubator/create-react-app/issues/2677
              ident: 'postcss',
              plugins: () => [
                require('postcss-flexbugs-fixes'),
                autoprefixer({
                  browsers: [
                    '>1%',
                    'last 4 versions',
                    'Firefox ESR',
                    'not ie < 9', // React doesn't support IE8 anyway
                  ],
                  flexbox: 'no-2009',
                }),
              ],
            },
          },
        ],
      },
      // "file" loader makes sure those assets get served by WebpackDevServer.
      // When you `import` an asset, you get its (virtual) filename.
      // In production, they would get copied to the `build` folder.
      // This loader doesn't use a "test" so it will catch all modules
      // that fall through the other loaders.
      {
        // Exclude `js` files to keep "css" loader working as it injects
        // it's runtime that would otherwise processed through "file" loader.
        // Also exclude `html` and `json` extensions so they get processed
        // by webpacks internal loaders.
        exclude: [/\.js$/, /\.html$/, /\.json$/],
        loader: require.resolve('file-loader'),
        options: {
          name: 'static/media/[name].[hash:8].[ext]',
        },
      },
    ],
  },
  // ** STOP ** Are you adding a new loader?
  // Make sure to add the new loader(s) before the "file" loader.
],

},
plugins: [

// Makes some environment variables available in index.html.
// The public URL is available as %PUBLIC_URL% in index.html, e.g.:
// <link rel="shortcut icon" href="%PUBLIC_URL%/favicon.ico">
// In development, this will be an empty string.
new InterpolateHtmlPlugin(env.raw),
// Generates an `index.html` file with the <script> injected.
new HtmlWebpackPlugin({
  inject: true,
  template: paths.appHtml,
}),
// Add module names to factory functions so they appear in browser profiler.
new webpack.NamedModulesPlugin(),
// Makes some environment variables available to the JS code, for example:
// if (process.env.NODE_ENV === 'development') { ... }. See `./env.js`.
new webpack.DefinePlugin(env.stringified),
// This is necessary to emit hot updates (currently CSS only):
new webpack.HotModuleReplacementPlugin(),
// Watcher doesn't work well if you mistype casing in a path so we use
// a plugin that prints an error when you attempt to do this.
// See https://github.com/facebookincubator/create-react-app/issues/240
new CaseSensitivePathsPlugin(),
// If you require a missing module and then `npm install` it, you still have
// to restart the development server for Webpack to discover it. This plugin
// makes the discovery automatic so you don't have to restart.
// See https://github.com/facebookincubator/create-react-app/issues/186
new WatchMissingNodeModulesPlugin(paths.appNodeModules),
// Moment.js is an extremely popular library that bundles large locale files
// by default due to how Webpack interprets its code. This is a practical
// solution that requires the user to opt into importing specific locales.
// https://github.com/jmblog/how-to-optimize-momentjs-with-webpack
// You can remove this if you don't use Moment.js:
new webpack.IgnorePlugin(/^\.\/locale$/, /moment$/),

],
// Some libraries import Node modules but don't use them in the browser.
// Tell Webpack to provide empty mocks for them so importing them works.
node: {

dgram: 'empty',
fs: 'empty',
net: 'empty',
tls: 'empty',
child_process: 'empty',

},
// Turn off performance hints during development because we don't do any
// splitting or minification in interest of speed. These warnings become
// cumbersome.
performance: {

hints: false,

},
};