Сделаем менюшку на PHP7:
Класс menu.php:

Код:
<?php
class Menu {
  private $str_id;
  private $arr_items;
  private $int_count;

  public function __construct($str_id) {
    $this->str_id = $str_id;
    $this->arr_items = array();
    $this->int_count = 0;
  }

  public function add_item($str_text, $str_url) {
    $this->arr_items[$this->int_count] = array('text' => $str_text, 'url' => $str_url);
    $this->int_count++;
  }

  public function render($arr_params = NULL) {
    $str_class_nav = '';
    $str_class_menu = '';
    $str_class_menu_item = '';
    $str_class_menu_anchor = '';
    if(is_array($arr_params)) {
      if(isset($arr_params['class_nav']))
        $str_class_nav = ' class="' . $arr_params['class_nav'] . '" ';
      if(isset($arr_params['class_menu']))
        $str_class_menu = ' class="' . $arr_params['class_menu'] . '" ';
      if(isset($arr_params['class_menu_item']))
        $str_class_menu_item = ' class="' . $arr_params['class_menu_item'] . '" ';
      if(isset($arr_params['class_menu_anchor']))
        $str_class_menu_anchor = ' class="' . $arr_params['class_menu_anchor'] . '" ';
    }

    $str_result = '<nav ' . $str_class_nav . 'id="' . $this->str_id . '"><ul' . $str_class_menu . '>';
    foreach($this->arr_items as $arr_item) 
      $str_result .= sprintf('<li' . $str_class_menu_item . '><a '. $str_class_menu_anchor . 'href="%s">%s</a></li>',  $arr_item['url'], $arr_item['text']);

    $str_result .= '</ul>';
    return $str_result;
  }
}
?>

Код index.php:

Код:
<?php
require_once('menu.php');

$mnu = new Menu('menu');
$mnu->add_item('Стартовая страница', 'index.php');
$mnu->add_item('Продукты', 'product.php');
$mnu->add_item('Контакт', 'contact.php');
$mnu->add_item('О нас', 'about.php');
?>

<!DOCTYPE html>
<html>
  <head>
    <title>Menu Demo</title>
    <style>
      .nav { background-color:blue; }
      .menu { list-style-type:none; margin:0; padding:0; overflow:hidden; }
      .menuitem { float:left; }
      .menuitem a { display:block; color:white; text-align: center; padding:10px 7px; text-decoration:none; border:1px solid blue;}
      .menuitem a:hover { background-color:white; color:blue; border:1px solid yellow;}
    </style>
  </head>
  <body>
    <?=$mnu->render(array('class_nav' => 'nav', 
                          'class_menu' => 'menu', 
                          'class_menu_item' => 'menuitem')); 
    ?>
  </body>
</html>

Результат:
https://i.ibb.co/DRYMbtj/horiz-menu-php7-23-30-09-10-2021-min.jpg