Banner image not covering page

Thanks for looking!

I'm a designer. It's my first go using Squarespace & the Brine template.

I have a page within an Index with a background banner image (just a slab of black in this case).

When I create a link to that page in the Footer Navigation the background banner no longer sits behind the whole page. Annoyingly it is contained within a strip across the top of the page, and the site-wide colour is the rest. (I've noticed this is the case for any page pulled from an Index that contains a full bleed banner image.)

How do I keep the banner background image behind the whole page?

I've used a little CSS to customise fonts, spacing, make the header sticky — nothing too tricky. When I delete all my CSS the problem still remains.

https://mela-draft.squarespace.com/config/pages

I've attached screen captures of the intended look (all-over black background) and the way it looks with just a strip at the top & the site-wide colour background (cream).

Solved:

When you create the link, copy the slug with a hashtag in front (not a forward slash). Ie:

#we-give-a-damn

Damn Squarespace 7 hours later! -- this should have been easier -- it's a basic function and is buried!!