https://cn.vuejs.org/v2/guide/instance.html - 【学习】-【安装】- section CDN
!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<!-- 引入 Vue，通过使用CDN -->
<script src="https://cdn.jsdelivr.net/npm/vue@2.6.14"></script>
</head>https://element.eleme.io/#/zh-CN/component/installation - 【组件】-【安装】-section CDN
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<!-- 引入CDN -->
<script src="https://cdn.jsdelivr.net/npm/vue@2.6.14"></script>
<!-- 引入Element UI样式 -->
<link rel="stylesheet" href="https://unpkg.com/element-ui/lib/theme-chalk/index.css">
<!-- 引入Element UI组件库 -->
<script src="https://unpkg.com/element-ui/lib/index.js"></script>
</head>
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>xxxxxxx</title>
<!--引入外部样式CSS文件-->
<link rel="stylesheet" href="./css/index.css">
<!--使用CDN，引入Vue模块-->
<script src="https://cdn.jsdelivr.net/npm/vue@2.6.14"></script>
<!--引入Element UI引入样式 -->
<link rel="stylesheet" href="https://unpkg.com/element-ui/lib/theme-chalk/index.css">
<!--引入Element UI引入组件库 -->
<script src="https://unpkg.com/element-ui/lib/index.js"></script>
<!--引入Axios实现Ajax请求 -->
<script src="https://unpkg.com/axios/dist/axios.min.js"></script>
</head><head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<!-- 引入本地CSS -->
<link rel="stylesheet" href="./css/index.css">
<!-- 引入CDN -->
<script src="https://cdn.jsdelivr.net/npm/vue@2.6.14"></script>
<!-- 引入Element UI样式 -->
<link rel="stylesheet" href="https://unpkg.com/element-ui/lib/theme-chalk/index.css">
<!-- 引入Element UI组件库 -->
<script src="https://unpkg.com/element-ui/lib/index.js"></script>
</head>备注：./css/index.css，其中“.”代表html所在文件夹。意思是，把html所在文件夹/css/index.css引入。