Source: dist/css/virtual_boot.css, line 8294
13.1.3.2 Favorite Button Small
The favorite button is a simple icon that can be used to add or remove a favorite. This button reflects the state of the favorite.
Example s
<a href="#" aria-label="mark as favorite" class="btn btn-secondary btn-sm flex_none a:bg_alert-n2 h:bg_alert-n4 [modifier]" ><i class="fas fa-heart"></i></a>