Shards

Alerts can be created using the .alert class combined with a contextual modifier class (e.g. .alert-primary).

<div class="alert alert-primary" role="alert">
  This is a primary alert—check it out!
</div>
<div class="alert alert-secondary" role="alert">
  This is a secondary alert—check it out!
</div>
<div class="alert alert-success" role="alert">
  This is a success alert—check it out!
</div>
<div class="alert alert-danger" role="alert">
  This is a danger alert—check it out!
</div>
<div class="alert alert-warning" role="alert">
  This is a warning alert—check it out!
</div>
<div class="alert alert-info" role="alert">
  This is a info alert—check it out!
</div>
<div class="alert alert-light" role="alert">
  This is a light alert—check it out!
</div>
<div class="alert alert-dark" role="alert">
  This is a dark alert—check it out!
</div>

Dismissible Alerts

You can also create dismissible alerts using the alert JavaScript plugin and by adding a dismiss button and by adding the .alert-dismissible class. You can learn more about alerts in the official Bootstrap 4 documentation.

<!-- Danger Dismissible Alert -->
<div class="alert alert-danger alert-dismissible fade show" role="alert">
  <button type="button" class="close" data-dismiss="alert" aria-label="Close">
    <span aria-hidden="true">&times;</span>
  </button>
  <strong>Oh no!</strong> Something terrible happened!
</div>

<!-- Warning Dismissible Alert -->
<div class="alert alert-warning alert-dismissible fade show" role="alert">
  <button type="button" class="close" data-dismiss="alert" aria-label="Close">
    <span aria-hidden="true">&times;</span>
  </button>
  <strong>Damn!</strong> Something not very terrible happened!
</div>

<!-- Success Dismissible Alert -->
<div class="alert alert-success alert-dismissible fade show" role="alert">
  <button type="button" class="close" data-dismiss="alert" aria-label="Close">
    <span aria-hidden="true">&times;</span>
  </button>
  <strong>Yay!</strong> Everything is fine!
</div>

Make sure you check out the official Bootstrap 4 documentation for more information on alert components.