Polymer elements added to third_party/polymer.

third_party/polymer/components/core-pages/core-pages.css

-<!--
+/*
 Copyright (c) 2014 The Polymer Project Authors. All rights reserved.
 This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
 The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
 The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
 Code distributed by Google as part of the polymer project is also
 subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
--->
+*/
 
-<link rel="import" href="layout.html">
+:host {
+  display: block;
+  position: relative;
+}
 
-<script src="polymer.js"></script>
-<!--<link rel="import" href="../polymer-dev/polymer.html">--> 
+polyfill-next-selector { content: ':host > *'; }
+::content > * {
+  position: absolute;
+  top: 0;
+  right: 0;
+  bottom: 0;
+  left: 0;
+  visibility: hidden;
+  z-index: -1000;
+}
+
+polyfill-next-selector { content: ':host > .core-selected'; }
+::content > .core-selected {
+  visibility: visible;
+  z-index: auto;
+}