more specifically, your style sheet and your program need to live in the same directory because of your  LINK declaration.

move (or copy) your stylesheet into your cgi-bin (which is where i'm assuming your script lives), and your styles will work. alternately, use a standard location for your styles ( say,  WEBROOT/css/ and have your  LINK reference that common directory.

the second approach will keep you from having to maintain multiple copies of the style sheet.