Decrease space (margin) between header menu & a section below

Site URL: https://aperitivojournal.squarespace.com/

Hi experts,

Please find the screenshot attached. I am trying to adjust the margin from the navigation menu to the (image) section below in the header by decreasing the margin.

My website is not published yet, so please find the screenshot below. (sorry) I've tried several CSS codes searched on this forum, but there was no luck yet.

Also it'd be really useful if I'd like to decrease the margin or padding of sections on pages. 

Could you help please? Thank you. 

Hi,

Your site is private. You can setup password & share url again. We can check easier