Use two different icons for expand/collapse

assets/js/lesson.js

@@ -8,13 +8,13 @@ $(".challenge,.solution").click(function(event) {
                || $(event.target).filter(".fold-unfold").size() > 0;
     if (trigger) {
         $(">*:not(h2)", this).toggle(400);
+        $(">h2>span.fold-unfold", this).toggleClass("glyphicon-collapse-down glyphicon-collapse-up");
     }
 });
 $(".challenge,.solution").each(function() {
     $(">*:not(h2)", this).toggle();
     var h2 = $("h2:first", this);
-    h2.append("<span class='fold-unfold glyphicon glyphicon-expand'></span>");
-
+    h2.append("<span class='fold-unfold glyphicon glyphicon-collapse-down'></span>");
 });