Simple to use external js file packed

surroundings

node + webpack4.0 + webpack-cli + style-loader css-loader

File Structure

│  1.png
│  package.json
│  webpack.config.js
│
└─src
    │  app.js
    │
    └─css
            t.css

package.json (dependent)

{
  "name": "loader",
  "version": "1.0.0",
  "description": "",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "css-loader": "^2.1.1",
    "style-loader": "^0.23.1",
    "webpack": "^4.33.0",
    "webpack-cli": "^3.3.3"
  }
}

Configuration package webpack

loader order must be style-css-loader then CSS 
File-loader 

url-loader

const path = require('path');
module.exports = {
    entry: {
        app: './src/app.js'
    },
    output: {
        filename: "bundle.js",
        path: path.join(path.resolve(__dirname), 'dist')
    },
    mode: "development",
    module: {
        rules: [
            {
                test: /\.js$/,
                exclude: '/node_modules/',
            },
            {
                test: /\.css$/,
                use: ["style-loader", "css-loader"] 
            }
        ]
    }
};