原因：创建项目的时候选择的是2.x版本，后续安装的less和less-loader开发依赖包版本号过高
解决：先删除原来安装的less和less-loader
命令： npm uninstall less-loader
npm uninstall less
再安装
npm install less-loader@4.1.0 -D
npm install less@3.9.0 -D
若在安装过程中控制台报如下错误：
npm ERR! code ERESOLVE
npm ERR! ERESOLVE unable to resolve dependency tree
npm ERR!
npm ERR! While resolving: vue_shop@0.1.0
npm ERR! Found: less@4.1.1
npm ERR! node_modules/less
npm ERR! dev less@"^4.1.1" from the root project
npm ERR!
npm ERR! Could not resolve dependency:
npm ERR! peer less@"^2.3.1 || ^3.0.0" from less-loader@4.1.0
npm ERR! node_modules/less-loader
npm ERR! dev less-loader@“4.1.0” from the root project
npm ERR!
npm ERR! Fix the upstream dependency conflict, or retry
npm ERR! this command with --force, or --legacy-peer-deps
npm ERR! to accept an incorrect (and potentially broken) dependency resolution.
npm ERR!
npm ERR! See C:\Users\ASUS\AppData\Local\npm-cache\eresolve-report.txt for a full report.

npm ERR! A complete log of this run can be found in:
npm ERR! C:\Users\ASUS\AppData\Local\npm-cache_logs\2021-09-25T08_19_08_654Z-debug.log
则在控制台输入如下命令：npm install npm@3.8.6 -g
成功解决