remove space between header image and menu

Since I turned my header image into an image map in order to be able to have multiple clickable areas, there is a gap between the header and the main menu bar.
I have tried to change various paddings and margins, but nothing changed.
I also tried setting the menu height from 45px to 48px and the gap was gone, instead there was a white stripe because the default menu background that came with my theme seems to be no higher than 45px.

Any tips on how to get rid of this space are highly appreciated 🙂

ps. I can’t provide a link to the blog since it’s not supposed to be visible to public yet. But if it’s any help – I’m using a Child Theme of Chip Life.