I note this in your page:
<base href="https://www. dmc - on - line . com/" />
https

and so its trying to get the css via https:....
While I would not have thought it would be a problem, Firefox->Web Developer->CSS->View CSS and clicking on a css file link yields an error as it cannot retrieve the file.

If I replicate this by changing my code from
PHP Code:
<base href="<?php echo (($request_type == 'SSL') ? HTTPS_SERVER . DIR_WS_HTTPS_CATALOG : HTTP_SERVER . DIR_WS_CATALOG ); ?>" />
to
PHP Code:
<base href="<?php echo (($request_type == 'SSL') ? HTTPS_SERVER . DIR_WS_HTTPS_CATALOG : HTTPS_SERVER . DIR_WS_CATALOG ); ?>" />
I see exactly the same problem.