To use a Bootstrap icon, for example, use the name according to the list of Bootstrap icons and add the prefix bi- in front of it. So, for example, bi-0-circle-fill instead of just 0-circle-fill. It is essential to add bi- in front of the name in order to identify the desired icon as a “Bootstrap icon.”
For an Awesome icon, use the name according to the list of Awesome icons with the prefix fa-. For example, fa-address-book instead of just address-book. Adding fa- before the name identifies the desired icon as a “Font Awesome icon.”
Other icon collections supported by Mercury use prefixes such as nf-, fab-, fas-, or far-.