[Can not access to the website and no content displayed]

I have deleted the database and recreated it then imported the sql file again. Now it worked. Thanks

[Can not access to the website and no content displayed]

Error message""

Warning: mysqli::__construct(): (HY000/1049): Unknown database 'app' in C:\xampp\htdocs\webapp\connection.php on line 2
Unable to connect to database [Unknown database 'app']

""

There are error message displayed when I go on to the website and it happens to all pages (PHP files). Below is the code on connection.php file"

<?php
    $db = new mysqli('localhost', 'root', '', 'app');
    ini_set ('display_errors', 'Off');
?>

""

Does anyone konw what is happening and how to fix this?

many thanks