安装sass, 建议用cnpm

cnpm install node-sass sass-loader -D

create-react-app 创建项目默认是没有配置文件的，所以你需要

npm run eject

// 之后会在当前目录有个 config文件夹

配置 webpack.config.dev.js，在 config/webpack.config.dev.js

搜索：rules 就能找到下面这些代码了，我已经注释了， 只要加入sass-loader 就好了

module: {
    strictExportPresence: true,
    rules: [
      {
        test: /\.(js|jsx)$/,
        enforce: 'pre',
        use: [
          {
            options: {
              formatter: eslintFormatter,
              eslintPath: require.resolve('eslint'),
              
            },
            loader: require.resolve('eslint-loader'),
          },
        ],
        include: paths.appSrc,
      },
      {
        oneOf: [
          {
            test: [/\.bmp$/, /\.gif$/, /\.jpe?g$/, /\.png$/],
            loader: require.resolve('url-loader'),
            options: {
              limit: 10000,
              name: 'static/media/[name].[hash:8].[ext]',
            },
          },
          {
            test: /\.(js|jsx)$/,
            include: paths.appSrc,
            loader: require.resolve('babel-loader'),
            options: {
              cacheDirectory: true,
            },
          },
          {
            test: /\.css$/,
            use: [
              require.resolve('style-loader'),
              {
                loader: require.resolve('css-loader'),
                options: {
                  importLoaders: 1,
                },
              },
              {
                loader: require.resolve('postcss-loader'),
                options: {
                  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',
                    }),
                  ],
                },
              },
            ],
          },
					// =======================  这里加入sass-loader Begin ================
          {
            test: /\.scss$/,
            loaders: ['style-loader', 'css-loader', 'sass-loader'],
          },
					// =======================  这里加入sass-loader End ================
		
          {
            exclude: [/\.js$/, /\.html$/, /\.json$/],
            loader: require.resolve('file-loader'),
            options: {
              name: 'static/media/[name].[hash:8].[ext]',
            },
          },
        ],
      },
    ],
  },

注意了上面的是开发环境的， 生产环境也需要配置，生产环境配置文件在config/webpack.config.prod.js，配置跟开发环境一模一样，只要按照上述配置就行了。