Default alert

<div class="alert alert-warning fade in">
    <button aria-hidden="true" data-dismiss="alert" class="close" type="button">×</button>
    <strong>Holy guacamole!</strong> Best check yo self, you're not looking too good. 
</div>

Error or danger

<div class="alert alert-danger fade in"> 
    <button aria-hidden="true" data-dismiss="alert" class="close" type="button">×</button> 
    <h4>Oh snap! You got an error!</h4> 
</div>

Success

<div class="alert alert-success fade in">
    <button aria-hidden="true" data-dismiss="alert" class="close" type="button">×</button>
    <strong>Well done!</strong>You successfully read this important alert message. 
</div>

Information

<div class="alert alert-info fade in">
    <button aria-hidden="true" data-dismiss="alert" class="close" type="button">×</button>
    <strong>Heads up!</strong> This alert needs your attention, but it's not super important.
</div>