How to set a background image url in CSS when my CI applications is into a subfolder?

[eluser]Optimus Prime[/eluser]
Thaks, your ideas and experience helped me a lot!

John: I pick your first option, to have a common folder in the root folder. But your modification for a Menu driven multiple CodeIgniter applications are great. I will post my comments for it.

Michael: Your folder structure is very useful. I think I will use your idea with some modifications for a commons template engine of all my site. In this way, the subfolder may be a name of a theme template and it will make more sense to have one more directory level.