LoginForm

<?php
    session_start();
    $greshka = false;
    if(isset($_POST['submit'])){
        $username = $_POST['uname'];
        $password = $_POST['psw'];
        if($username == 'Ivan' && $password == '12345678'){
            $_SESSION['logged'] = $username;
            header('location: index.html');
        }else{
            $greshka = 'wrong username';
        }
    }
?>

<form action="loginform.php" method="post">
  <div class="container">
    <label for="uname"><b>Username</b></label>
    <input type="text" placeholder="Enter Username" name="uname" required>

    <label for="psw"><b>Password</b></label>
    <input type="password" placeholder="Enter Password" name="psw" required>

    <button type="submit" id="submit" name="submit">Login</button>
    <label>
      <input type="checkbox" checked="checked" name="remember"> Remember me
    </label>
  </div>

  <div class="container" style="background-color:rgb(225, 225, 225)">
    <button type="button" class="cancelbtn">Cancel</button>
    <span class="psw">Forgot <a href="#">password?</a></span>
  </div>
</form>

<?php
if($greshka){

?>
    <div>
        <h1><?= $greshka?></h1>
    </div>
<?php
}
?>