bootstrap相关

链接

bootstrap4安装和CDN: https://v4.bootcss.com/
bootstrap4组建: https://v4.bootcss.com/docs/components/alerts/

bootstrap3安装和CDN: https://v3.bootcss.com/getting-started/
bootstrap3全局样式: https://v3.bootcss.com/css/#images
bootstrap3组建: https://v3.bootcss.com/components/#btn-groups

w3school：http://www.w3school.com.cn/jquery/index.asp