Your sliders element rs-module-wrap
has a z-index of 1.
There is no z-index on your nav
element. So at this moment the nav
element will stay below the slider.
Setting the z-index to 2 for example on your nav
element will solve this, because the higher z-index will push your nav to the top.
This works because these 2 elements are currently relatively positioned to the same parent which is body.
Not sure what the dark grey background is for, but it makes the links not easy to read. But maybe it is just for testing.
Good luck!
Jeroen