Re-configured samples page.

src/site/samples/todo/index.markdown

+---
+layout: default
+title: Adding elements to the DOM
+live_example_url: /docs/tutorials/add-elements/examples/todo/todo.html
+header:
+  css: ["/samples/samples.css"]
+---
+
+## {{ page.title }}
+
+Enter text in the input field and press return.
+
+This app shows how to programmatically add an element to the DOM.
+
+In this example, when you press return, the event handler for the input
+field creates a new <li> element and adds it to an existing <ul> list in the
+DOM tree. When the DOM tree changes, the web page refreshes.
+
+Read this [tutorial](/docs/tutorials/add-elements/) for
+more detail, or read the
+[source](https://github.com/dart-lang/dart-tutorials-samples/tree/master/web/todo).
+
+<iframe class="running-app-frame"
+        style="height:400px;width:40%;"
+        src="{{page.live_example_url}}">
+</iframe>
+
+See all [samples](/samples/)