private static function errorHtml($statusCode, $message)
{
return <<<EOT
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Error {$statusCode}</title>
<style>html{font-family: sans-serif;}</style>
<meta name="viewport" content="width=device-width, initial-scale=1">
</head>
<body>
<h1>Error {$statusCode}</h1>
{$message}
</body>
</html>
EOT;
}