Banner placement and top menu

Hi, I’m unable to get my banners at the top of my pages to be positioned correctly for both desktop and laptops. I’ve altered the margins for responsive too. There is a line where the bottom of the top menu meets/doesn’t meet the banner image.

I am concerned because it is difficult to get this looking right on the devices I own, and I am aware that it is likely to look wrong for other people. Is there something I can do that will fix this problem so that the banner is always neatly up against the top menu?

I’ll post screenshots and login info in a private message below.

Thanks for your time!