WordPress login using a completely custom page and no plugins?

If you’re happy to do a bit of coding, then start by creating a new page template for your login page, name a file something like page-login.php in your themes root and make that page markup how you want it.

Once you have the mark-up in place, add in the following tag, which will pull in the WP login form onto the page for you.

<?php wp_login_form(); ?>
<a href="<?php echo wp_lostpassword_url(); ?>" class="btn secondary">Forgotten Password?</a>

If it’s the markup of the form itself that you want to change, I don’t believe you can. But, doing the above will give you the facility to add custom styling, CSS, JS, to the page if required.