PHP form - Registration Successful Message on New Page

Question

After each entry has been verified, the registration form I built sends some information to the database and brings users to the login page.

However, I would like to see something like this on the login page: Registration Was Successful. Please Log In.

if (!validated() {
    // post error messages

} else {
    echo '
       <div class="container">
        <div class="page-header">
            <h3>Registration Complete</h3>
        </div>
       </div>';

    header( 'Location: ../login.php' );
}

Login file :

Header - Navbar

<div class="container">
   <div class="page-header">
       <h3>Login To Members Corner</h3>
   </div>

   <form>
       // login form
   </form>

Footer

Can someone please help me with this?