bootstrap警告框

bootstrap中警告框用div承载
在div添加class
.alert 表示这是一个警告框

<div class="alert ">警告框</div>

##警告框样式
.alert-primary
.alert-secondary
.alert-success
.alert-danger
.alert-warning
.alert-info
.alert-light
.alert-dark

<div class="alert alert-primary" role="alert">
    A simple primary alert—check it out!
</div>
<div class="alert alert-secondary" role="alert">
    A simple secondary alert—check it out!
</div>
<div class="alert alert-success" role="alert">
    A simple success alert—check it out!
</div>
<div class="alert alert-danger" role="alert">
    A simple danger alert—check it out!
</div>
<div class="alert alert-warning" role="alert">
    A simple warning alert—check it out!
</div>
<div class="alert alert-info" role="alert">
    A simple info alert—check it out!
</div>
<div class="alert alert-light" role="alert">
    A simple light alert—check it out!
</div>
<div class="alert alert-dark" role="alert">
    A simple dark alert—check it out!
</div>