if (isset($_POST['login'])) {

    $username = mysqli_real_escape_string($con, $_POST['username']);
    $password = mysqli_real_escape_string($con, $_POST['password']);
    $result = mysqli_query($con, "SELECT * FROM users WHERE username = '$username' and password = '$password'");

    if ($row = mysqli_fetch_array($result)) {
        $_SESSION['uuid'] = $row['uuid'];
        $_SESSION['username'] = $row['username'];
        $_SESSION['password'] = $row['password'];
        $_SESSION['email'] = $row['email'];
        $_SESSION['group'] = $row['group'];
        session_start();
        header("Location: index.php");
    } else {
        $errormsg = "<font color='#444444'>
                        <i class='fa fa-times-circle'></i>
                        Nebyl nalezen žádný uživatelský účet se zadanými údaji
                    </font>";
    }
}