怎样创建一个警告框 ？
为 <div> 添加 .alert 类，同时还要从下面的类中选择一个样式： .alert-success .alert-info .alert-warning .alert-danger
<div class = "alert alert-success">Success! Well done its submitted.</div>
<div class = "alert alert-info">Info! take this info.</div>
<div class = "alert alert-warning">Warning ! Dont submit this.</div>
<div class = "alert alert-danger">Error ! Change few things.</div>
01.PNG
怎样为警告框添加一个关闭按钮 ？
在警告框内部添加一个 <button> ，同时给作为警告框的 <div> 增加一个 .alert-dismissable 类，
<div class = "alert alert-success alert-dismissable">
<button type = "button" class = "close" data-dismiss = "alert" aria-hidden = "true">
×
</button>
Success! Well done its submitted.
</div>
......
02.PNG
如何在警告框中添加链接 ？
正常在警告框中添加 <a> 即可，不过要为 <a> 增加 .alert-link 类
<div class = "alert alert-success">
<a href = "#" class = "alert-link">Success! Well done its submitted.</a>
</div>
......
03.PNG
