Mainnav : how to center mainnav position and add module in the same row

Hello,

I hope not everybody is on the beach !
I would be gratefull if someone could help for those 2 questions:
. how to center mainnav (dropline menu), I don't find the css solution
. how to add 2 modules on the same mainnav row, like this (with mainnav centered):
POSITION-1 MAINNAV POSITION-2

Many thanks.

Xavier