Index: wp-content/themes/twentytwelve/style.css
===================================================================
--- wp-content/themes/twentytwelve/style.css	(revision 21588)
+++ wp-content/themes/twentytwelve/style.css	(working copy)
@@ -531,9 +531,11 @@
 .main-navigation a:hover {
 	color: #21759b;
 }
-.main-navigation .menu {
+.main-navigation ul.nav-menu,
+.main-navigation div.nav-menu ul {
 	display: none;
 }
+.main-navigation ul.nav-menu.toggled-on,
 .menu-toggle {
 	display: inline-block;
 }
@@ -1340,7 +1342,7 @@
 		font-size: 1.857142857rem;
 		line-height: 1.846153846;
 	}
-	.main-navigation .menu {
+	.main-navigation ul.nav-menu {
 		border-bottom: 1px solid #ededed;
 		border-top: 1px solid #ededed;
 		display: inline-block !important;
@@ -1548,7 +1550,7 @@
 	.site-content nav,
 	.widget-area,
 	img.header-image,
-	nav.site-navigation {
+	.main-navigation {
 		display: none;
 	}
 	.wrapper {
Index: wp-content/themes/twentytwelve/js/navigation.js
===================================================================
--- wp-content/themes/twentytwelve/js/navigation.js	(revision 21588)
+++ wp-content/themes/twentytwelve/js/navigation.js	(working copy)
@@ -3,14 +3,17 @@
  *
  * Handles toggling the navigation menu for small screens.
  */
+( function() {
+	var button = document.getElementById( 'site-navigation' ).getElementsByTagName( 'h3' )[0],
+	    menu   = document.getElementById( 'site-navigation' ).getElementsByTagName( 'ul' )[0];
 
-jQuery( document ).ready( function( $ ) {
-	if ( ! $( '#masthead .menu' ).children().length ) {
-		$( '#masthead .menu-toggle' ).hide();
-	}
-
-	$( '.menu-toggle' ).off( 'click' ).click( function() {
-		$( '#masthead .menu' ).stop().slideToggle();
-		$( this ).toggleClass( 'toggled-on' );
-	} );
-} );
\ No newline at end of file
+	button.onclick = function() {
+		if ( button.className.match( new RegExp( '(\\s|^)toggled-on(\\s|$)' ) ) ) {
+			button.className = 'menu-toggle';
+			menu.className = 'nav-menu';
+		} else {
+			button.className= 'menu-toggle toggled-on';
+			menu.className = 'nav-menu toggled-on';
+		}
+	};
+} )();
\ No newline at end of file
Index: wp-content/themes/twentytwelve/header.php
===================================================================
--- wp-content/themes/twentytwelve/header.php	(revision 21588)
+++ wp-content/themes/twentytwelve/header.php	(working copy)
@@ -35,10 +35,10 @@
 			<h2 class="site-description"><?php bloginfo( 'description' ); ?></h2>
 		</hgroup>
 
-		<nav class="site-navigation main-navigation" role="navigation">
+		<nav id="site-navigation" class="main-navigation" role="navigation">
 			<h3 class="menu-toggle"><?php _e( 'Show menu', 'twentytwelve' ); ?></h3>
 			<div class="skip-link assistive-text"><a href="#content" title="<?php esc_attr_e( 'Skip to content', 'twentytwelve' ); ?>"><?php _e( 'Skip to content', 'twentytwelve' ); ?></a></div>
-			<?php wp_nav_menu( array( 'theme_location' => 'primary' ) ); ?>
+			<?php wp_nav_menu( array( 'theme_location' => 'primary', 'menu_class' => 'nav-menu' ) ); ?>
 		</nav>
 
 		<?php $header_image = get_header_image();