the newcomer, in the process of building according to the steps on the Internet, the following error occurred:

paste the configuration file about less code:
/ / webpack.config.dev.js

{

        test: [/\.css$/, /\.less$/],
        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",
                }),
              ],
            },
          },
          {
            loader: require.resolve("less-loader"), // compiles Less to CSS
          }
        ],
      },
          
          

/ / webpack.config.prod.js

{
            // modify
            test: /\.(css|less)$/,
            loader: ExtractTextPlugin.extract(
              Object.assign(
                {
                  fallback: {
                    loader: require.resolve("style-loader"),
                    options: {
                      hmr: false,
                    },
                  },
                  use: [
                    {
                      loader: require.resolve("css-loader"),
                      options: {
                        importLoaders: 1,
                        minimize: true,
                        sourceMap: shouldUseSourceMap,
                      },
                    },
                    {
                      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",
                          }),
                        ],
                      },
                    },
                    {
                      //add
                      loader: require.resolve("less-loader"),
                    }
                  ],
                },
                extractTextPluginOptions
              )
            ),
            // Note: this won"t work without `new ExtractTextPlugin()` in `plugins`.
          }
         

/ / index.js

import React from "react";
import ReactDOM from "react-dom";
// import { Router } from "react-router-dom";
import CRouter from "./routers/routeMap";
import { AppContainer } from "react-hot-loader";
import { Provider } from "react-redux";
import { createStore } from "redux";
import registerServiceWorker from "./registerServiceWorker";
import SideCustom from "./containers/side/SiderCustom";
import HeadContain from "./containers/header/header";
import indexReducer from "./reducers/index";
import App from "./App";
import "antd/dist/antd.css";
import "./index.css";