update elements and fix some bugs

lib/src/iron-component-page/iron-component-page.css

 /**
 @license
 Copyright (c) 2015 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
 
 */
@@ skipping 61 matching lines @@
   @apply(--layout-fit);
 }
 
 #nodocs {
   background: var(--paper-grey-50);
   font-size: 24px;
   font-weight: 400;
   color: var(--paper-grey-400);
 }
 
-#demo {
+#demo,
+#demo iframe {
   border: 0;
   background: transparent;
   width: 100%;
   height: 100%;
   overflow-x: none;
   overflow-y: auto;
 }
 
 #view > * {
   display: none;
 }
 
 #view > .iron-selected {
   display: block;
 }
 
 #docs {
+  max-width: var(--iron-component-page-max-width, 48em);
+  @apply(--iron-component-page-container);
   padding: 20px;
-  max-width: 48em;
   margin: 0 auto;
 }
 
 #active {
   font-size: 20px;
   font-family: Roboto, Noto;
   border: 0;
   background: transparent;
 }
 
@@ skipping 34 matching lines @@
 [catalog-only] {
   display: none;
 }
 
 :host([_catalog]) [catalog-only] {
   display: block;
 }
 :host([_catalog]) [catalog-hidden] {
   display: none;
 }