Icons

Joomla uses free FontAwesome icons, which are implemented as CSS pseudo-elements

The list of icons which are available can be found in media/templates/administrator/atum/css/vendor/fontawesome-free.css

The subset of FontAwesome icons which are used internally within Joomla are designated as "icon-something", for example, "icon-file" is used to display a file icon.

To display such an icon you can use:

?>
<span class="icon-cancel"></span> <?php echo Text::_('JCANCEL') ?> 

You can also display FontAwesome icons which aren't used in Joomla, but you have to include the "fa" class:

?>
<span class="fa fa-bomb"></span> <?php echo Text::_('JSAVE') ?>