Warning: Undefined variable $conn in C:\xampp\htdocs\nurimcocom\doc\admin\config.php on line 2

Fatal error: Uncaught TypeError: mysqli_query(): Argument #1 ($mysql) must be of type mysqli, null given in C:\xampp\htdocs\nurimcocom\doc\admin\config.php:2 Stack trace: #0 C:\xampp\htdocs\nurimcocom\doc\admin\config.php(2): mysqli_query(NULL, 'SELECT * FROM s...') #1 C:\xampp\htdocs\nurimcocom\doc\view\header.php(2): include('C:\\xampp\\htdocs...') #2 C:\xampp\htdocs\nurimcocom\doc\_index.php(2): include('C:\\xampp\\htdocs...') #3 {main} thrown in C:\xampp\htdocs\nurimcocom\doc\admin\config.php on line 2