Webpack configuration does not create CSS files from SCSS/LESS - wordpress

Question

I'm using the following WordPress starter plugin with a full working Vue configuration implemented: https://github.com/tareq1988/vue-wp-starter
This plugin works in general. But seems that there is a Webpack issue which is responsible to generate some css files.
This is the Webpack configuration:
const webpack = require("webpack");
const path = require("path");
const package = require("./package.json");
const { VueLoaderPlugin } = require("vue-loader");
const HtmlWebpackPlugin = require("html-webpack-plugin");
const BrowserSyncPlugin = require("browser-sync-webpack-plugin");
const TerserJSPlugin = require("terser-webpack-plugin");
const MiniCssExtractPlugin = require("mini-css-extract-plugin");
const OptimizeCSSAssetsPlugin = require("optimize-css-assets-webpack-plugin");
const config = require("./config.json");
const devMode = process.env.NODE_ENV !== "production";
// Naming and path settings
var appName = "app";
var entryPoint = {
frontend: "./src/frontend/main.js",
admin: "./src/admin/main.js",
style: ['./assets/less/style.less', './assets/scss/style.scss'],
};
var exportPath = path.resolve(__dirname, "./assets/js");
// Enviroment flag
var plugins = [];
// extract css into its own file
plugins.push(
new MiniCssExtractPlugin({
filename: "../css/[name].css",
ignoreOrder: true
})
);
plugins.push(
new webpack.DefinePlugin({
__VUE_OPTIONS_API__: false,
__VUE_PROD_DEVTOOLS__: false,
}),
)
// enable live reload with browser-sync
// set your WordPress site URL in config.json
// file and uncomment the snippet below.
// --------------------------------------
// plugins.push(new BrowserSyncPlugin( {
// proxy: {
// target: config.proxyURL
// },
// files: [
// '**/*.php'
// ],
// cors: true,
// reloadDelay: 0
// } ));
plugins.push(new VueLoaderPlugin());
// Differ settings based on production flag
if (devMode) {
appName = "[name].js";
} else {
appName = "[name].min.js";
}
module.exports = {
entry: entryPoint,
mode: devMode ? "development" : "production",
output: {
path: exportPath,
filename: appName,
},
resolve: {
alias: {
vue$: "vue/dist/vue.esm-bundler.js",
"#": path.resolve("./src/"),
frontend: path.resolve("./src/frontend/"),
admin: path.resolve("./src/admin/"),
},
modules: [
path.resolve("./node_modules"),
path.resolve(path.join(__dirname, "src/")),
],
},
optimization: {
runtimeChunk: "single",
splitChunks: {
cacheGroups: {
vendor: {
test: /[\\\/]node_modules[\\\/]/,
name: "vendors",
chunks: "all",
},
},
},
minimizer: [new TerserJSPlugin({}), new OptimizeCSSAssetsPlugin({})],
},
plugins,
module: {
rules: [
{
test: /\.vue$/,
loader: "vue-loader",
},
{
test: /\.js$/,
use: "babel-loader",
exclude: /node_modules/,
},
{
test: /\.less$/,
use: ['vue-style-loader', "css-loader", "less-loader"],
},
{
test: /\.scss$/,
use: [
'vue-style-loader',
'css-loader',
'sass-loader'
]
},
{
test: /\.png$/,
use: [
{
loader: "url-loader",
options: {
mimetype: "image/png",
},
},
],
},
{
test: /\.svg$/,
use: "file-loader",
},
{
test: /\.css$/,
use: [
{
loader: MiniCssExtractPlugin.loader,
options: {
publicPath: (resourcePath, context) => {
return path.relative(path.dirname(resourcePath), context) + "/";
},
hmr: process.env.NODE_ENV === "development",
},
},
"css-loader",
],
},
],
},
};
This is the folder structure for the relevant part:
Starting the app with npm run dev I get no error messages. But I expect the files /assets/css/admin.css and /assets/css/frontend.css to automatically be created. This is what the developer says here:
Also the paths are included in the related PHP files for WordPress (includes/Assets.php):
So I get the following 404 error:
....plugin-root/assets/css/admin.css?ver=0.1.0 net::ERR_ABORTED 404 (Not Found)
Long description in short: The configurator for this starter plugin should generate two css files which are missing. What could be the reason for this? Do I miss something?