Bootstrap CSS bg-success alert not working

I just spent all day trying to figure out why alert-error wasn't working, only to realize it's not alert-error, it's alert-danger. Leaving this here in case someone else tortures themselves for hours trying to figure out what's wrong with their Bootstrap 3 alert.

In Bootstrap you have the following pre-defined backgrounds:

Bootstrap 3.1.0:

<div class="bg-primary">...</div>
<div class="bg-success">...</div>
<div class="bg-info">...</div>
<div class="bg-warning">...</div>
<div class="bg-danger">...</div>

Bootstrap 3.0.3:

<div class="alert alert-success">...</div>
<div class="alert alert-info">...</div>
<div class="alert alert-warning">...</div>
<div class="alert alert-danger">...</div>

Bootstrap components

View all Bootstrap components here

Contextual backgrounds bg-primary, bg-success, bg-info, bg-warning and bg-danger were added to Bootstrap as of version 3.1.0 and were not present in 3.0.3 and before.

There have however been alerts with the four contextual classes alert-success, alert-info, alert-warning and alert-danger which are suitable for that kind of error messages.

<p class="alert alert-danger">There was an error updating your details.</p>

Also see the Bootstrap Alerts Component: http://getbootstrap.com/components/#alerts