Creating my CSS and XHTML

Please help me, I need some advice, I have built a website in dreamweaver for a friend, its all published on the internet with its own domain name but my friend doesn’t know html and css so I was hoping wordpress can help. I have installed wordpress and uploaded it to my server along with the database for it, my question is how do i go about putting the website I have already built to work through wordpress so my friend can just change and update the basics of what i have already done, I need to be able to change the css to the styles I already have for it, id this possible, can anyone help me?