z-index, header and navigation

Hiya,

So I was mighty proud to have worked out that if I increased the z-index of the header of a site I am building for a client, that I could get the logo to sit just a tiny bit over the menu. But now the menu doesn’t work. I am assuming this is because the header is taking precedence over the menu. Am I right, and does anyone know of anyway around this?

URL is: https://www.emaentertainment.com.au/
Theme is Abundance by https://www.kreisi.at

Thanks in advance ??
Bridie