Untitled

<html>
<center>
<h1> <strong> Register Page </strong> </h1>
<style>

body{
    background-color: #FF0000;
}
</style>

<?php

 if(ISSET($_POST['login'])){
    header('Location:login.php');

if(ISSET($_POST['submitButton'])){
    $fname = $_POST['firstname'];
    $lname = $_POST['lastname'];
    $email = $_POST['email'];
    $username = $_POST['username'];
    $password = $_POST['password'];
    $hash = password_hash($password, PASSWORD_DEFAULT);

    require('conn.php');
    $query = "INSERT INTO `users` (`users_id`, `fname`, `lname`, `email`, `username`, `password`) VALUES (NULL, '$fname', '$lname', '$email', '$username', '$hash');";
    mysqli_query($conn,$query) or DIE('Bad query');
    echo "GG, you registered.";
    ?>
    <form method="POST" action="<?php echo $_SERVER['PHP_SELF']; ?>">
    <br><br>
    <br><br>
    <input type="submit" name = "login" value = "Login">
    <?php
     if(ISSET($_POST['login'])){
        header('Location:login.php');
    }
} else{
?>
<body>
        <strong>
<form method="POST" action="<?php echo $_SERVER['PHP_SELF']; ?>">
    first name:
    <input type ="text" name="firstname" value="fname">
    <br><br>
    last name:
    <input type ="text" name="lastname" value="lname">
    <br><br>
    email:
    <input type ="text" name="email" value="E-mail">
    <br><br>
    username:
    <input type ="text" name="username" value="Username">
    <br><br>
    password:
    <input type ="text" name="password" value="Password">
    <br><br>

    <input type="submit" name = "submitButton" value = "Submit">
    <br><br>
    <?php
    echo "already logged in?"
    ?>
    <br><br>
    <input type="submit" name = "login" value = "Login">
</form>
<?php } ?>
</body>
</html>