You can use the custom css section in the ACP to customize it, just give the navigation items a custom class in the class field. Then use css to target that.
How to reset the navigation on ACL
I have remove all menu items.
Now, how I can reset the navigation, because Drag&Drop from ACL doesn't work if navigation bar empty.
I'm using NodeBB 1.1.2
Thanks for reporting it is fixed on master now.