fix(overlay): demo拆解与规范

[Alex-huxiyang]

🤔 这个变动的性质是？

• 新特性提交
• 日常 bug 修复
• 站点、文档改进
• 演示代码改进
• 组件样式/交互改进
• TypeScript 定义更新
• 包体积优化
• 性能优化
• 功能增强
• 国际化改进
• 重构
• 代码风格优化
• 测试用例
• 分支合并
• 其他改动（是关于什么的改动？）

🔗 相关 Issue

💡 需求背景和解决方案

☑️ 请求合并前的自查清单

⚠️ 请自检并全部勾选全部选项。⚠️

• 文档已补充或无须补充
• 代码演示已提供或无须提供
• TypeScript 定义已补充或无须补充
• fork仓库代码是否为最新避免文件冲突
• Files changed 没有 package.json lock 等无关文件

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.47%. Comparing base (d60fa15) to head (2cde28b).

Additional details and impacted files

@@           Coverage Diff           @@
##             next    #2012   +/-   ##
=======================================
  Coverage   77.47%   77.47%           
=======================================
  Files         215      215           
  Lines        8980     8980           
  Branches     2684     2684           
=======================================
  Hits         6957     6957           
  Misses       1832     1832           
  Partials      191      191           

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