If you never edit the css, you can use the regular options to customize your event box
However, if you ever edit the css, it seems to adopt the visual options (background pattern/colour/animation/etc) that you were using at the time. You cannot change these, and then edit the css after while keeping the new visual settings. They revert back to whatever they were when you edited the event box.
I'd like to be able to reset the event box widget to its default settings, as if it's never been used/changed.