twenty_twenty_one_add_sub_menu_toggle( string $output, object $item, int $depth, object $args ): string

27function twenty_twenty_one_add_sub_menu_toggle( $output, $item, $depth, $args ) {28	if ( 'primary' === $args->theme_location29		&& 0 === $depth && in_array( 'menu-item-has-children', $item->classes, true )30	) {31 32		// Add toggle button.33		$output .= '<button class="sub-menu-toggle" aria-expanded="false" onClick="twentytwentyoneExpandSubMenu(this)">';34		$output .= '<span class="icon-plus">' . twenty_twenty_one_get_icon_svg( 'ui', 'plus', 18 ) . '</span>';35		$output .= '<span class="icon-minus">' . twenty_twenty_one_get_icon_svg( 'ui', 'minus', 18 ) . '</span>';36		/* translators: Hidden accessibility text. */37		$output .= '<span class="screen-reader-text">' . esc_html__( 'Open menu', 'twentytwentyone' ) . '</span>';38		$output .= '</button>';39	}40	return $output;41}