add assets

assets/fontawesomefree/js-packages/@fortawesome/fontawesome-free/less/_mixins.less

@@ -40,3 +40,34 @@
     .fa-sr-only();
   }
 }
+
+// convenience mixins for declaring pseudo-elements by CSS variable,
+// including all style-specific font properties, and both the ::before
+// and ::after elements in the duotone case.
+.fa-icon-solid(@fa-var) {
+  .fa-icon;
+  .fa-solid;
+
+  &::before {
+    content: @fa-var;
+  }
+}
+
+.fa-icon-regular(@fa-var) {
+  .fa-icon;
+  .fa-regular;
+
+  &::before {
+    content: @fa-var;
+  }
+}
+
+.fa-icon-brands(@fa-var) {
+  .fa-icon;
+  .fa-brands;
+
+  &::before {
+    content: @fa-var;
+  }
+}
+