Font Awesome Size 1.5. Rem stands for “root em” because it calculates the size based on the size of the root of the document or body tag. Font awesome, the iconic font and css framework.
In fact, moodle already uses font awesome! Updated font awesome to 4.5.0; Font awesome, the iconic font and css framework.
If you're interested in font awesome 4, follow this link.
Using both versions on the same page. Font awesome 5 has a pro edition with 7842 icons, and a free edition with 1588 icons. Font awesome is just a font so you can use the font size attribute in your css to change the size of the icon. Introduced 3 additional shortcode for font awesome 5+ still support font awesome 4;
