How can PHP developers ensure that included menus are seamlessly integrated with the overall design of their site?

To ensure that included menus are seamlessly integrated with the overall design of a site, PHP developers can use a templating system like Smarty or Twig. These systems allow developers to separate the logic of the menu from the design, making it easier to maintain and update the menu without affecting the overall layout of the site.

// Example using Smarty templating system
$smarty = new Smarty;
$smarty->assign('menuItems', $menuItems);
$smarty->display('menu.tpl');
```

```php
// Example using Twig templating system
$loader = new Twig_Loader_Filesystem('templates');
$twig = new Twig_Environment($loader);
echo $twig->render('menu.twig', ['menuItems' => $menuItems]);