there is a slight inconsistency in how the icons for predefined elements are setup.
E.g. in "Buttons" there is sth. like:
<i class="b-fa-folder-open b-fa"> </i>
.b-tree-leaf-cell .b-tree-cell-inner:before, .b-tree-expander:before, .b-tree-icon:before {
font-family: "Font Awesome 5 Pro";
color: #adaeaf;
}
In this case there is also the problem, that "b-tree-expander" is hard coded and cannot be configured by extending the class. Even when defining a custom icon, the ":before" overrules the common
.b-fa { font-familiy:"xxx"}