fontawesome.com facebook icon code example
Example 1: fa fa-facebook
<i class="fa fa-facebook-square" aria-hidden="true"></i>
Example 2: font awesome facebook
Font Awesome 5:
Letter F: <i class="fab fa-facebook-f"></i>
Round: <i class="fab fa-facebook"></i>
Square: <i class="fab fa-facebook-square"></i>
Messenger: <i class="fab fa-facebook-messenger"></i>