Alert – Customized alerts using the BootstrapComponents extension.

From Bootstrap - Demo Wiki
Component
Name Alert
Description Customized alerts using the BootstrapComponents extension.
Provider BootstrapComponents
Reference BootstrapComponents Extension docs - alert
Styling For all possible color styles and corresponding examples, see colors.

Custom inline CSS

Code
<bootstrap_alert style="border-radius: 2rem;">This alert has a round border.</bootstrap_alert>
Result

Custom CSS class

Code
<bootstrap_alert class="bootstrap-alert-example">This alert has a dashed border.</bootstrap_alert>

On MediaWiki:Common.css or MediaWiki:Chameleon.css:

.bootstrap-alert-example {
  border: 1px dashed black;
}
Result