* All buttons should be wrapped in a `<div class="btn-group">` in order to receive their proper vertical and horizontal spacing.
* Use the `.btn-` classes on the `<a>`, `<button>`, or `<input>` tags.
* `.btn-primary` indicates the primary action.
* `.btn-secondary` indicates the default action.
* `.btn-link` is used when the user needs a lighter-weight appearance.
* `.btn-success`, `.btn-info`, `.btn-warning`, and `.btn-danger` are optional classes that come from Bootstrap.
* The `disabled` attribute can be applied to the `<a>`, `<button>`, or `<input>` tags.
* The `.active` class can be applied to the `<a>` tag to pre-select a button.