I would like to apply some special styling to header when user is on homepage.
It is not difficult to test if he is somewhere else...

For instance:

if (action='vthread') ...; tests whether he is on posts page.

if($action=='userinfo') tests whether he is in profile page

if ($forum==3) test whether he is on page that belongs to some specific forum ID3


But how to test that he sees homepage (forums list and last discussions lis)?
Would you know?

I tried excluding all pages but home one, but that does not work, as some of them are not identifiable either (like some during register process - after captcha, updating profile, etc.) and this way it would be much more time consuming for server (too many questions if? if? if?).

Please help.

if($action=='')

parhaps. As I said some steps have now actions attached and stil they are not hompege. During register process - after captcha, updating profile, any actually some of those Error messages, but, well,... but the action may be hidden right? OK, let me try.

$action is always present and it exactly defines the operation type user is trying to execute, so above recommendation should work for you.

OK, thanks. It does work!