Add Informational Message Below the Username Field in the Login/Register Form #The Greek

function add_custom_message_to_username_field() {

    ?>

    <script type="text/javascript">

        document.addEventListener('DOMContentLoaded', function() {

            var usernameFields = document.querySelectorAll('input[name="username"]');

            usernameFields.forEach(function(usernameField) {

                var messageDiv = document.createElement('div');

                messageDiv.style.color = 'red';

                messageDiv.style.fontWeight = 'bold';

                messageDiv.style.marginBottom = '10px';

                messageDiv.innerHTML = 'Here you are setting your message that you want to preview to login form/ Register form.';

                usernameField.parentNode.insertBefore(messageDiv, usernameField);

            });

        });

    </script>

    <?php

}

add_action('wp_footer', 'add_custom_message_to_username_field');