404 page chrome
Custom not-found title, body HTML, and background under Design → Downloads (not Pages).
404 page chrome
Customizes the public not-found experience (app/not-found).
Where to find it
Admin → Design → Downloads → 404 (/admin/design/download/404) - not under Pages
Setting key: design.download.not_found_page_v1
How it works
Page title text (default Four Hundred and Four, max 120) and alignment. Page body TipTap (default sorry copy + home link). Page background fill plus optional image.
Empty body HTML is restored to the default on parse. If title/body still match the English defaults, the live page can swap in locale strings.
Site header/footer still wrap the page; this only paints the not-found content area.
Common problems
Looking under Pages
404 lives in the Downloads Design group.
Nearly empty 404
Body was cleared then refilled with defaults - edit and save your copy.