diff -r 48c4eec2b7e6 -r 8c2e4d02f4ef wp/wp-includes/class-wp-customize-nav-menus.php
--- a/wp/wp-includes/class-wp-customize-nav-menus.php	Fri Sep 05 18:40:08 2025 +0200
+++ b/wp/wp-includes/class-wp-customize-nav-menus.php	Fri Sep 05 18:52:52 2025 +0200
@@ -1222,21 +1222,15 @@
 		$id = sprintf( 'available-menu-items-%s-%s', $available_item_type['type'], $available_item_type['object'] );
 		?>
 		<div id="<?php echo esc_attr( $id ); ?>" class="accordion-section">
-			<h4 class="accordion-section-title" role="presentation">
-				<?php echo esc_html( $available_item_type['title'] ); ?>
-				<span class="spinner"></span>
-				<span class="no-items"><?php _e( 'No items' ); ?></span>
-				<button type="button" class="button-link" aria-expanded="false">
-					<span class="screen-reader-text">
-					<?php
-						/* translators: %s: Title of a section with menu items. */
-						printf( __( 'Toggle section: %s' ), esc_html( $available_item_type['title'] ) );
-					?>
-						</span>
+			<h4 class="accordion-section-title">
+				<button type="button" class="accordion-trigger" aria-expanded="false" aria-controls="<?php echo esc_attr( $id ); ?>-content">
+					<?php echo esc_html( $available_item_type['title'] ); ?>
+					<span class="spinner"></span>
+					<span class="no-items"><?php _e( 'No items' ); ?></span>
 					<span class="toggle-indicator" aria-hidden="true"></span>
 				</button>
 			</h4>
-			<div class="accordion-section-content">
+			<div class="accordion-section-content" id="<?php echo esc_attr( $id ); ?>-content">
 				<?php if ( 'post_type' === $available_item_type['type'] ) : ?>
 					<?php $post_type_obj = get_post_type_object( $available_item_type['object'] ); ?>
 					<?php if ( current_user_can( $post_type_obj->cap->create_posts ) && current_user_can( $post_type_obj->cap->publish_posts ) ) : ?>
@@ -1263,27 +1257,23 @@
 	protected function print_custom_links_available_menu_item() {
 		?>
 		<div id="new-custom-menu-item" class="accordion-section">
-			<h4 class="accordion-section-title" role="presentation">
-				<?php _e( 'Custom Links' ); ?>
-				<button type="button" class="button-link" aria-expanded="false">
-					<span class="screen-reader-text">
-						<?php
-						/* translators: Hidden accessibility text. */
-						_e( 'Toggle section: Custom Links' );
-						?>
-					</span>
+			<h4 class="accordion-section-title">
+				<button type="button" class="accordion-trigger" aria-expanded="false" aria-controls="new-custom-menu-item-content">
+					<?php _e( 'Custom Links' ); ?>
 					<span class="toggle-indicator" aria-hidden="true"></span>
 				</button>
 			</h4>
-			<div class="accordion-section-content customlinkdiv">
+			<div class="accordion-section-content customlinkdiv" id="new-custom-menu-item-content">
 				<input type="hidden" value="custom" id="custom-menu-item-type" name="menu-item[-1][menu-item-type]" />
 				<p id="menu-item-url-wrap" class="wp-clearfix">
 					<label class="howto" for="custom-menu-item-url"><?php _e( 'URL' ); ?></label>
 					<input id="custom-menu-item-url" name="menu-item[-1][menu-item-url]" type="text" class="code menu-item-textbox" placeholder="https://">
+					<span id="custom-url-error" class="error-message" style="display: none;"><?php _e( 'Please provide a valid link.' ); ?></span>
 				</p>
 				<p id="menu-item-name-wrap" class="wp-clearfix">
 					<label class="howto" for="custom-menu-item-name"><?php _e( 'Link Text' ); ?></label>
 					<input id="custom-menu-item-name" name="menu-item[-1][menu-item-title]" type="text" class="regular-text menu-item-textbox">
+					<span id="custom-name-error" class="error-message" style="display: none;"><?php _e( 'The link text cannot be empty.' ); ?></span>
 				</p>
 				<p class="button-controls">
 					<span class="add-to-menu">