What you actually inherit

Inheriting from a parent theme in Dune isn't block-level template inheritance — it's whole-file fallback, resolved child → parent for a few specific things:

• templates/*.tsx — any template a child theme doesn't define falls back to the one here. Define blog.tsx in your own theme and only that file is overridden; search.tsx, error.tsx, and the rest still resolve to this package's copies.
• components/layout.tsx — the Layout prop every template receives resolves through the same chain. A child that ships its own layout gets it automatically threaded into every inherited template too.
• locales/*.json — merged per key. A child overriding one string doesn't need to copy the rest.

Two things deliberately don't inherit: config_schema in theme.yaml (the admin UI only reads the active theme's manifest — copy over the keys your templates actually reference), and mdx-components.ts (Dune loads only the active theme's file; re-export and extend the base one if you want its components too).

The theme's own README has the full breakdown, including the two patterns for building on top of this — restyling the base outright, or borrowing just the behavioral templates (search, error, section) inside a fully independent layout.