How to separate css files in webpack?

Question

npm

Started disassembling webpack, and ran into a problem. For example, in the index.js file, I include normalize and bootstrap.css, but they are combined into one vendors~main.css file. How to separate them?

Code with webpack.config.js

const path = require('path');
const HtmlWebpackPlugin = require('html-webpack-plugin');
const { CleanWebpackPlugin } = require('clean-webpack-plugin');
const MiniCssExtractPlugin = require('mini-css-extract-plugin');
const CopyPlugin = require('copy-webpack-plugin');

const isDev = process.env.NODE_ENV === "development";
const isProd = process.env.NODE_ENV === "production";

module.exports = {
  mode: 'development', // метод по умолчанию
  // context: path.resolve(__dirname, "src"), // папка исходных файлов
  entry: {
    main: ["@babel/polyfill", './src/index.js'],
  },
  output: {
    filename: '[name].js',
    path: path.resolve(__dirname, 'assets'),
  },
  resolve: {
    alias: {
      "@": path.resolve(__dirname, "src"), // теперь @ - ссылка на путь корневой папки, если прописывать в import в index.js
    }
  },
  optimization: {
    splitChunks: {
      // chunks: "all", // разделить подключенные файлы
      cacheGroups: {
        styles: {
          name: 'styles',
          test: /\.css$/,
          chunks: 'all',
          enforce: true,
        },
      },
    }
  },
  devtool: 'inline-source-map',
  devServer: {
    contentBase: './assets',
  },
  plugins: [
    new CleanWebpackPlugin(),
    new HtmlWebpackPlugin({
      template: "./src/index.html",
      minify: {
        collapseWhitespace: isProd,
      }
    }),
    new MiniCssExtractPlugin({
      filename: '/styles/css/[name].css',
      chunkFilename: '/styles/css/[name].css',
    }),
    new CopyPlugin([
      { from: 'src/styles/scss/', to: 'styles/scss/' },
      // { from: 'src/fonts/', to: 'fonts/' },
      // { from: 'src/images/', to: 'images/' },
      // { from: 'src/files/', to: 'files/' },
    ]),
  ],
  module: {
    rules: [
      {
        test: /\.js$/,
        exclude: /node_modules/,
        loader: {
          loader: "babel-loader",
          options: {
            presets: [
              "@babel/preset-env"
            ]
          }
        }
      },
      {
        test: /\.css$/,
        use: [
          MiniCssExtractPlugin.loader,
          'css-loader',
          {
            loader: "postcss-loader",
            options: {
              sourceMap: true,
              config: {
                path: "src/js-config/postcss.config.js"
              }
            }
          },
        ],
      },
      {
        test: /\.s[ac]ss$/i,
        use: [
          'style-loader',
          MiniCssExtractPlugin.loader,
          {
            loader: 'css-loader',
            options: {
              sourceMap: true,
            },
          },
          {
            loader: "postcss-loader",
            options: {
              sourceMap: true,
              config: {
                path: "src/js-config/postcss.config.js"
              }
            }
          },
          {
            loader: 'sass-loader',
            options: {
              sourceMap: true,
            },
          },
        ],
      },
      {
        test: /\.(png|svg|jpg|jpeg|gif)$/,
        use: [
          'file-loader',
        ],
      },
      {
        test: /\.(woff|woff2|eot|ttf|otf)$/,
        use: [
          {
            loader: 'file-loader',
            options: {
              // context: 'public',
              name: 'assets/images/[name].[ext]?v=[hash]',
              // publicPath: './',
            },
          },
        ],
      },
      {
        test: /\.(csv|tsv)$/,
        use: [
          'csv-loader',
        ],
      },
      {
        test: /\.xml$/,
        use: [
          'xml-loader',
        ],
      },
    ],
  },
};