The open iconic icons used in salt haven't been updated in 10 years. The project looks abandoned.
Please switch to Bootstrap icons https://icons.getbootstrap.com/ which are maintained actively and have more much icons to use. See also https://github.com/twbs/icons
The Bootstrap icons can be offered as e.g. <$icon-name> or <%icon-name> so backwards compatibility for the open iconic icons remains via <&icon-name>
