Getting out side of wp root folder from function.php using absolute path

If you want the absolute path to your theme’s stylesheet directory you could use get_stylesheet_directory(). If you want the URI of your theme’s stylesheet directory you could use get_stylesheet_directory_uri().

get_theme_root() will return the absolute path to the themes directory.

get_home_path() will return the absolute filesystem path to the root of the WordPress installation.

Once you’ve got your absolute path with one of these methods you can then do what you need to do.