Excess space before menu

I'm refurbing an old website built with Catch Base Pro, using a new license. Viewed on a desktop browser, there is excess space between header image and menu bar, which disappears when the browser window becomes small enough to trigger the mobile menu (hamburger icon).  I am NOT displaying Site Title, Tagline or Logo, but using a header image across the entire site. I've tried some of the fixes for similar problems reported many years ago, without success.  Can you please advise? https://troonold.org.uk   [WP 6.3.2  Catch Base Pro 4.4.4]