I think we need to see the external style sheet. And you are not calling it in your code.
You have a lot of errors in your code, mostly using depreciated in-line styles that should be part of the css; like <center> <font> and stuff.
You also have two <html> tags and two extra </div> tags at the end of your code.
My suggestion would be to re=code the html section without in-line styles and fix the errors then add the external style sheet lastly add your own to tweak things and not start with your stylings.