add assets

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

@@ -40,3 +40,34 @@
     @include 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.
+@mixin fa-icon-solid($fa-var) {
+  @extend %fa-icon;
+  @extend .fa-solid;
+
+  &::before {
+    content: unquote("\"#{ $fa-var }\"");
+  }
+}
+
+@mixin fa-icon-regular($fa-var) {
+  @extend %fa-icon;
+  @extend .fa-regular;
+
+  &::before {
+    content: unquote("\"#{ $fa-var }\"");
+  }
+}
+
+@mixin fa-icon-brands($fa-var) {
+  @extend %fa-icon;
+  @extend .fa-brands;
+
+  &::before {
+    content: unquote("\"#{ $fa-var }\"");
+  }
+}
+