edit pass on T3,4,5, updated images

src/site/docs/tutorials/add-elements/examples/todo/todo.dart

+import 'dart:html';
+
+InputElement toDoInput;
+UListElement toDoList;
+
+void main() {
+  toDoInput = query('#to-do-input');
+  toDoList = query('#to-do-list');
+  toDoInput.onChange.listen(addToDoItem);
+}
+
+void addToDoItem(Event e) {
+  var newToDo = new LIElement();
+  newToDo.text = toDoInput.value;
+  toDoInput.value = '';
+  toDoList.children.add(newToDo);
+}