Don't take this personally, but you must be joking me....
All you have to do is to take the code I provided above and adjust it for your needs...come on, man... (don't do just copy and paste)
Set the left and right margins for the
SidebarMenuListItem to center it into the div container.
If that's not working, then set the margins to the
SidebarMenuList to center it.
this is the way I position all my inner containers in the parent containers,
so it should work
Cheers.