1.使用npm i vant@latest-v2 -S 命令安装，（我当时没有仔细看，在vue2中用的是vue3的命令，结果就是一直报错）

   vue3 使用npm i vant -S 命令安装

2.需要安装babel插件 --babel-plugin-import

指令:npm i babel-plugin-import -D (简写)

3.babel.config.js文件中写入

module.exports = {
  presets: [
    '@vue/cli-plugin-babel/preset'
  ],
  plugins: [
        ["import", {
          "libraryName": "vant",
          "libraryDirectory": "es",
          "style": true
        }]
      ]

}

4.在main.js中

import { Button } from 'vant'
// import 'vant/lib/index.css';
Vue.use(Button)

5.在对应组件中输入

 <van-button type="primary">主要按钮</van-button>
<van-button type="success">成功按钮</van-button>
<van-button type="default">默认按钮</van-button>
<van-button type="warning">警告按钮</van-button>
<van-button type="danger">危险按钮</van-button>

二、这一部分是移动端rem的配置

npm i -S amfe-flexible

在main.js中导入import "amfe-flexible";

 npm install postcss postcss-pxtorem --save-dev

// postcss.config.js
module.exports = {
    plugins: {
      'postcss-pxtorem': {
        rootValue: 37.5,
        propList: ['*'],
      },
    },
  };

三、安装autoprefixer

安装时

1. 前置依赖安装

npm install -D css-loader style-loader

2. 安装postcss依赖相关依赖

npm install -D postcss-loader autoprefixer postcss

在此之前安装了less-loader，就疯了，疯狂报错，我把less-loader的版本调整到5.0，一直说webpack和less-loader版本不匹配，然后我就按照下图摆烂，居然好了...

npm remove less-loader
npm install [email protected]
npm install [email protected] --legacy-peer-deps

package.json文件的相关版本
  "dependencies": {
    "amfe-flexible": "^2.2.1",
    "core-js": "^3.8.3",
    "less-loader": "^5.0.0",
    "vant": "^2.12.51",
    "vue": "^2.6.14"
  },
 "devDependencies": {
    "@babel/core": "^7.12.16",
    "@babel/eslint-parser": "^7.12.16",
    "@vue/cli-plugin-babel": "~5.0.0",
    "@vue/cli-plugin-eslint": "~5.0.0",
    "@vue/cli-service": "~5.0.0",
    "autoprefixer": "^10.4.13",
    "babel-plugin-import": "^1.13.5",
    "css-loader": "^6.7.1",
    "eslint": "^7.32.0",
    "eslint-plugin-vue": "^8.0.3",
    "less": "^4.1.3",
    "postcss": "^8.4.18",
    "postcss-loader": "^7.0.1",
    "postcss-pxtorem": "^6.0.0",
    "style-loader": "^3.3.1",
    "vue-template-compiler": "^2.6.14"