Art Gallery Page - More intrinsic design

Another attempt at intrinsic design. I think the layout is mostly working OK but have two issues that have flummoxed me that I would welcome advice on:

• The h1 should be white on the black background, and black otherwise. I have tried following some online tutorials using mix-blend-mode for this but cannot make it work.
• For some reason, object-fit and object-postioning don't seem to have any impact on the map image. This is only really obvious on large screens, but again, I am a bit unsure of what I am doing wrong here.

EDIT:

• I just check how this looks on Safari - oh dear, some very storage behaviour going on in the header on the home page.
• And I realised I forgot to do the srcset for mobile images. That is probably my least favourite part of HTML, so I think I'm going to leave it. It's not where I wanted to focus with this one!
• And having just looked at the design and my attempt, I think I need to focus a bit more on combining this approach with 'pixel pretty close' if not perfect. I am way out here.