How to Hide Custom CSS, JS & PHP Admin Menus

function plt_hide_custom_css_menus() {
	//Hide the "Tools → Custom CSS" menu.
	remove_submenu_page('tools.php', 'alg-custom-css');
	//Hide the "Tools → Custom JS" menu.
	remove_submenu_page('tools.php', 'alg-custom-js');
	//Hide the "Tools → Custom PHP" menu.
	remove_submenu_page('tools.php', 'alg-custom-php');
}

add_action('admin_menu', 'plt_hide_custom_css_menus', 11);

Where do I put this code?