Where can I extend the max padding

I'm not sure if this belongs to panels or ctools....

When I create a custom style for my panes the largest value for padding I can choose is 3.95em. Unfortunately I need more ...
I tried to find the code where that is declared to extend it with no luck...
I checked the css folders in both panels and ctools directory but couldn't find it.
Firebug didn't help either.

So please ... Merlin or somebody else point me to the right file.

Thx Qriz