Aligning Submenu to parent item when fullwidth

i want to use the fullwidth menu option, when i do, the submenu aligns completely to the left. i would like it to be aligned to the parent item conserving the background as fullwidth. Can you please help with this?

Hi
I see... this is a special request. You could probably do that with CSS but actually I have not tested.
The fact is that the submenu, is fullwidth from the left of the menu, or naturally aligned under the parent item
Both behavior has never been tested by me

CEd