Error 404 menu links don't update in subfolders

I use php in all my files including my error 404 file so it has the same navigation as the rest of the site. My problem is, while my 404 works when the error is on mydomain.com/wherever, the css style sheet isn't called when the error is on mydomain.com/subfolder/wherever

How can I fix this? Thanks.


EDIT: Actually it doesn't call the css style file. The links work. Here are a working and nonworking 404 on my site:
Working: cineweekly.com/404.php (http://www.cineweekly.com/404.php)
Non Working: cineweekly.com/sunday/dfghljkgsn (http://www.cineweekly.com/sunday/dfghljkgsn)

I fixed it by adding a / on the 404 page:

<link href="/core-style.css" rel="stylesheet" type="text/css" />