[Plugin: JQuery Mega Menu Widget] How to center sub-container below menu-item

Actually, the sub-container position is wedged to the menu edges (left and right). And it seems to be done by the javascript itself.
I have a need : each sub-container should be centered beside their related menu-item (li).
How can I achieve that ?

Thanks a lot for your help

https://www.ads-software.com/extend/plugins/jquery-mega-menu/