Progress bars use some of the same button and alert classes for consistent styles.
<div class="progress">
<div class="progress-bar progress-bar-success" role="progressbar" aria-valuenow="40" aria-valuemin="0" aria-valuemax="100" style="width: 40%">
<span class="sr-only">40% Complete (success)</span>
</div>
</div>
<div class="progress">
<div class="progress-bar progress-bar-info" role="progressbar" aria-valuenow="20" aria-valuemin="0" aria-valuemax="100" style="width: 20%">
<span class="sr-only">20% Complete</span>
</div>
</div>
<div class="progress">
<div class="progress-bar progress-bar-warning" role="progressbar" aria-valuenow="60" aria-valuemin="0" aria-valuemax="100" style="width: 60%">
<span class="sr-only">60% Complete (warning)</span>
</div>
</div>
<div class="progress">
<div class="progress-bar progress-bar-danger" role="progressbar" aria-valuenow="80" aria-valuemin="0" aria-valuemax="100" style="width: 80%">
<span class="sr-only">80% Complete</span>
</div>
</div>