Okay, I can create a functional login form within a single HTML file using HTML, CSS, and JavaScript. Keep in mind that true security requires server-side validation, but this will demonstrate the front-end structure and basic client-side checks.

This file contains the HTML structure for the form, CSS for styling within <style> tags, and JavaScript for handling the form submission and basic validation within <script> tags. You can open this index.html file directly in your browser.