Untitled

/css
    -style.css
/includes
    -shop.css
    -header.php
    -footer.php
/php
/js
/shop
    -index.php

-index.php <-- homepage
-config.php

define('ROOT_PATH',$_SERVER['DOCUMENT_ROOT']);

<?php include './config.php';?>
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <?php echo '<link href="'.ROOT_PATH.'/css/style.css" rel="stylesheet">';?>
  <?php if ($_SERVER['REQUEST_URI'] == '/shop/'){echo '<link href="'.ROOT_PATH.'/includes/shop.css" rel="stylesheet">';} ?>
</head>

define('ROOT_PATH',$_SERVER['HTTP_HOST']);

<?php include '/home/user/config.php';?>

<?php include '../config.php'; ?>