mysqli ERROR: Unable to connect: SQLSTATE[HY000] [2002] No connection could be made because the target machine actively refused it code example

Example: mysqli_connect(): (hy000/2002): no connection could be made because the target machine actively refused it.

If you look at your XAMPP Control Panel, it's clearly stated that the port to the MySQL server is 3306 - you provided 3360. The 3306 is default, and thus doesn't need to be specified. Even so, the 5th parameter of mysqli_connect() is the port, which is where it should be specified.

You could just remove the port specification altogether, as you're using the default port, making it

$dbhost = 'localhost';
$dbuser = 'root';
$dbpass = '';
$db     = 'test_db13';
References

mysqli_connect()
Standard connection of MySQL