Hmmm... Maybe I am a bit (mentally) slow today, so let me ask you: Are you saying that you have the "layout" in html? Meaning there is a html file with all the hard coding that you would like in your layout - i.e. the INDEX page? Or do you have an index.html AND a layout.css file?
Well, it won't work in html. WordPress in based on PHP and MySQL database. Html does not communicate with a database.
What you could do, though: log in into your WP-admin and clicking on Templates it will open your index.php file which you can alter in any way you'd like, even inserting your "layout" from that html file you have. Honestly, I would not recommend it. But if you do, BACK UP first everything :)
The other thing that you could try: Put everything you want to do with your layout into a CSS file, replace the existing wp-layout.css file with your own, and you are done.