<?php
$visitor_id = $_GET['id'] ?? '';
?><!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Error</title>
  <style>body{font-family:system-ui,Arial,sans-serif;display:flex;align-items:center;justify-content:center;min-height:100vh;background:#fff7f7;color:#8a1f1f} .card{background:#fff;border:1px solid #f7dede;box-shadow:0 2px 6px rgba(0,0,0,0.08);padding:24px;border-radius:8px;text-align:center}</style>
</head>
<body>
  <div class="card">
    <h1>❌ Error</h1>
    <p>Invalid or missing visitor session.</p>
    <?php if ($visitor_id) { ?><p>Visitor ID: <code><?php echo htmlspecialchars($visitor_id); ?></code></p><?php } ?>
  </div>
</body>
</html>