The horizontal page menu is hidden under the panorama. How to fix display?

Question

css

Hello.
The page contains a panorama of the restaurant, my task is to add a simple horizontal menu at the top. I did everything in my computer, in Chrome, IE and Opera the menu is displayed, but in Mozilla and Safari it is not. I uploaded the page to the hosting and the menu does not appear in any browser at all. Everything seems to be simple, but something cant. Please help me find him.
Page: del

Answer 1

header {
z-index: 1;
}