I made a sign up and login form using PHP. Would love some feedback

Hey guys! This is my first attempt building something more complex. I built this from scratch and I’d love to know what there’s still to improve and what’s good already. The project is hosted on[GitHub ](https://github.com/andrekato1/signuploginform).

The HTML is fine for the most part, though I think my CSS looks pretty bad and messy. Any tips and/or feedback will be greatly appreciated. Thank you <3