提醒基本示例

<div class="container">
  <h2>Alerts</h2>
  <div class="alert alert-success">
    <strong>Success!</strong>
  </div>
  <div class="alert alert-info">
    <strong>Info!</strong>
  </div>
  <div class="alert alert-warning">
    <strong>Warning!</strong> All foelds are required
  </div>
  <div class="alert alert-danger">
    The username is required and can't be empty
  </div>
</div>