Index: src/wp-admin/css/customize-nav-menus.css
===================================================================
--- src/wp-admin/css/customize-nav-menus.css	(revision 32858)
+++ src/wp-admin/css/customize-nav-menus.css	(working copy)
@@ -223,7 +223,8 @@
 }
 
 /* Duplicates `.nav-menus-php .item-edit:before {}` in common.css:2220. */
-.wp-customizer .menu-item .item-edit:before {
+.wp-customizer .menu-item .item-edit:before,
+#available-menu-items .accordion-section-title button:after {
 	top: -1px;
 	right: 0;
 	content: '\f140';
@@ -241,7 +242,8 @@
 	text-decoration: none !important;
 }
 
-.wp-customizer .menu-item.menu-item-edit-active .item-edit:before {
+.wp-customizer .menu-item.menu-item-edit-active .item-edit:before,
+#available-menu-items .open .accordion-section-title button:after {
 	content: '\f142';
 }
 
@@ -599,14 +601,25 @@
 	background: #fff;
 }
 
+#available-menu-items .accordion-section-title button {
+	width: 30px;
+	height: 35px;
+	position: absolute;
+	top: 5px;
+	right: 5px;
+	z-index: 1;
+	cursor: pointer;
+}
+
+#available-menu-items .accordion-section-title button:focus {
+	-webkit-box-shadow: 0 0 0 1px #5b9dd9, 0 0 2px 1px rgba(30, 140, 190, .8);
+	box-shadow: 0 0 0 1px #5b9dd9, 0 0 2px 1px rgba(30, 140, 190, .8);
+}
+
 #available-menu-items .open .accordion-section-title {
 	background: #eee;
 }
 
-#available-menu-items .open .accordion-section-title:after {
-	content: '\f142';
-}
-
 #available-menu-items .accordion-section-content {
 	overflow-y: auto;
 	max-height: 200px; /* This gets set in JS to fit the screen size, and based on # of sections. */
@@ -625,18 +638,6 @@
 	margin: 0;
 }
 
-#available-menu-items .accordion-section-title button:focus:before {
-	display: block;
-	content: "";
-	width: 28px;
-	height: 32px;
-	position: absolute;
-	right: 5px;
-	top: 5px;
-	-webkit-box-shadow: 0 0 0 1px #5b9dd9, 0 0 2px 1px rgba(30, 140, 190, .8);
-	box-shadow: 0 0 0 1px #5b9dd9, 0 0 2px 1px rgba(30, 140, 190, .8);
-}
-
 #available-menu-items .accordion-section-content {
 	padding: 1px 15px 15px 15px;
 	min-height: 120px;
@@ -756,8 +757,9 @@
 	box-sizing: border-box;
 }
 
+#available-menu-items .accordion-section-title:after,
 #available-menu-items-search .accordion-section-title:after {
-	display: none;
+	content: none;
 }
 
 #available-menu-items-search .accordion-section-content:empty {
Index: src/wp-includes/class-wp-customize-nav-menus.php
===================================================================
--- src/wp-includes/class-wp-customize-nav-menus.php	(revision 32858)
+++ src/wp-includes/class-wp-customize-nav-menus.php	(working copy)
@@ -563,8 +563,8 @@
 				<dl class="menu-item-bar">
 					<dt class="menu-item-handle">
 						<span class="item-type">{{ data.type_label }}</span>
-						<span class="item-title">{{ data.title || wp.customize.Menus.data.l10n.untitled }}</span>
-						<button type="button" class="not-a-button item-add"><span class="screen-reader-text"><?php _e( 'Add Menu Item' ) ?></span></button>
+						<span class="item-title" id="menu-item-tpl-{{ data.id }}-title">{{ data.title || wp.customize.Menus.data.l10n.untitled }}</span>
+						<button type="button" class="not-a-button item-add" aria-describedby="menu-item-tpl-{{ data.id }}-title"><span class="screen-reader-text"><?php _e( 'Add Menu Item' ) ?></span></button>
 					</dt>
 				</dl>
 			</div>
@@ -625,7 +625,7 @@
 				<div class="accordion-section-content" data-type="search"></div>
 			</div>
 			<div id="new-custom-menu-item" class="accordion-section">
-				<h4 class="accordion-section-title"><?php _e( 'Links' ); ?><button type="button" class="not-a-button"><span class="screen-reader-text"><?php _e( 'Toggle' ); ?></span></button></h4>
+				<h4 class="accordion-section-title"><span id="section-title-links"><?php _e( 'Links' ); ?></span><button type="button" class="not-a-button" aria-describedby="section-title-links"><span class="screen-reader-text"><?php _e( 'Toggle' ); ?></span></button></h4>
 				<div class="accordion-section-content">
 					<input type="hidden" value="custom" id="custom-menu-item-type" name="menu-item[-1][menu-item-type]" />
 					<p id="menu-item-url-wrap">
@@ -657,7 +657,7 @@
 				foreach ( $post_types as $type ) :
 					?>
 					<div id="available-menu-items-<?php echo esc_attr( $type->name ); ?>" class="accordion-section">
-						<h4 class="accordion-section-title"><?php echo esc_html( $type->label ); ?> <span class="spinner"></span> <button type="button" class="not-a-button"><span class="screen-reader-text"><?php _e( 'Toggle' ); ?></span></button></h4>
+						<h4 class="accordion-section-title"><span id="section-title-<?php echo esc_attr( $type->label ); ?>"><?php echo esc_html( $type->label ); ?></span> <span class="spinner"></span> <button type="button" class="not-a-button" aria-describedby="section-title-<?php echo esc_attr( $type->label ); ?>"><span class="screen-reader-text"><?php _e( 'Toggle' ); ?></span></button></h4>
 						<div class="accordion-section-content" data-type="<?php echo esc_attr( $type->name ); ?>" data-obj_type="post_type"></div>
 					</div>
 				<?php
@@ -669,7 +669,7 @@
 				foreach ( $taxonomies as $tax ) :
 					?>
 					<div id="available-menu-items-<?php echo esc_attr( $tax->name ); ?>" class="accordion-section">
-						<h4 class="accordion-section-title"><?php echo esc_html( $tax->label ); ?> <span class="spinner"></span> <button type="button" class="not-a-button"><span class="screen-reader-text"><?php _e( 'Toggle' ); ?></span></button></h4>
+						<h4 class="accordion-section-title"><span id="section-title-<?php echo esc_attr( $tax->label ); ?>"><?php echo esc_html( $tax->label ); ?></span> <span class="spinner"></span> <button type="button" class="not-a-button" aria-describedby="section-title-<?php echo esc_attr( $tax->label ); ?>"><span class="screen-reader-text"><?php _e( 'Toggle' ); ?></span></button></h4>
 						<div class="accordion-section-content" data-type="<?php echo esc_attr( $tax->name ); ?>" data-obj_type="taxonomy"></div>
 					</div>
 				<?php