<?php
class db{
    public $host = 'localhost';
    public $username = 'root';
    public $password = '';
    public $dbname = 'oop';

    public function __construct(){
        $con = new mysqli($this->host,$this->username,$this->password,$this->dbname);
    }
}
if(isset($con)){
    echo "<center><h1 style='color:green;'>Db is conected</h1></center>";
}else{
    echo "<center><h1 style='color:red;'>Db is not conected</h1></center>";
}
$obj = new db;
?>