<h1><center>Please login </center></h1>
<form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="post">
    Username: <input type="text" name="user_n">
    Password: <input type="text" name="pass_w">
<input type="submit" name="submit" value="Submit Form">
</form>
<?php
    if(isset($_POST["submit"])){
    $user_n = $_POST["user_n"];
    $pass_w = $_POST["pass_w"];
    $db_user = "mon_user";
    $db_password = "mon_pass";
    $db_database = "sqli";
    $db_local = "localhost";
    $dat = new mysqli($db_local, $db_user, $db_password, $db_database);
    $query ="select secret_mess from users where Username=\"$user_n\" and Password=\"$pass_w\";";
    echo $query;
    $response = $dat->query($query);
    $row = $response->fetch_assoc();
    foreach($row as $item){
        echo "This is your secret message: $item";
    }
    $dat->close();
}
?>