You can make any div an alert box by adding alert alert-* classes to it. To add alert boxes to your page/post, you must be in the ‘Text’ editor view.

Examples

ClassSample Code
alert-success
<div class="alert alert-success" role="alert">Success!</div>
alert-info
<div class="alert alert-info" role="alert">Information.</div>
alert-warning
<div class="alert alert-warning" role="alert">Warning.</div>
alert-danger
<div class="alert alert-danger" role="alert">Danger!</div>