Thank you pal so much. It is working now

. Correction though: the URL of catbg.jpg should be:
../Forum_Images/, since such folder resides outside SE folder.
Nevertheless, I can't get it. If this was the reason, then why it was working fine the first time I accessed it? I haven't touched this area of declaration! I'm sure of that. Anyway, it doesn't matter as long as it's OK now.
So, it has nothing to do with this 'Transparent' attribute as I thought?
Once again, appreciate the effort Ali

. Many thanks.
Shall I remove the test account now?
Salam.