Center Menu( placing menu in center)

Hello, am still new here and am using https://tesseracttheme.com/ my website is moukadem.com. Although i have gone through the forum for similar issues, i wasnt able to solve it, since themes differ in tags and names of elements, my aim is to center my top/header menu and be able to put spaces in between them, in fact i want it to start from the very left for the first menu item and end at the very right (taking the whole width) , also the menu drop down appears BEHIND the cenetered image, how can i bring it to front.
i hope someone can help. thanks in advance.