Since YouTube update the chat,
my tutorial and CSS code no longer work.
I'm not going to update my code.
Instead, I'm now using this: http://chatv2.septapus.com/
It is way better than I've done before.
You can easily customise your own chat-room,
Font style, color, size, avatar size.
Just give it a try.
Thank all of you for using my method before.