In font awesome 4 you could easily apply an icon to a :before/:after element using CSS.
Is the same possible with the new font awesome 5 JS/SVG implementation? As fr
Should you be using Fort Awesome to serve your icons then you need to add font-family: , no need to use font-weight: 400/900.
font-family:
font-weight: 400/900
For more info see this link:
https://articles.fortawesome.com/how-to-using-fort-awesome-icons-f50ab11a2d2a