feat: migrate to nimbus

.github/dependabot.yml

@@ -16,11 +16,10 @@ updates:
         patterns:
           - "astro"
           - "@astrojs/*"
-          - "starlight-*"
-      expressive-code:
+          - "@cloudflare/nimbus-docs"
+      docs-search:
         patterns:
-          - "@expressive-code/*"
-          - "*expressive-code*"
+          - "pagefind"
       eslint:
         patterns:
           - "eslint"

.github/workflows/ci.yaml

@@ -31,23 +31,8 @@ jobs:
           node-version-file: ".nvmrc"
           cache: npm
 
-      - name: Run rumdl
-        uses: rvben/rumdl@9faf4696d56c0cff426a2f85b3fd476ebe0d0ec0 # v0.2.52
-        with:
-          version: 0.2.9
-          path: "."
-          fail-on-error: true
-
       - name: Install dependencies
         run: npm ci
 
-      - name: Run Check
-        run: npm run check
-
-      - name: Run linter
-        # npm run lint includes lint:markdown which is already handled bby the rumdl
-        # step above
-        run: npm run lint:src
-
-      - name: Run linkcheck
-        run: npm run linkcheck
+      - name: Validate
+        run: npm run validate

.gitignore

@@ -4,6 +4,7 @@ dist/
 
 # generated types
 .astro/
+.nimbus/
 
 # dependencies
 node_modules/

.prettierignore

@@ -2,7 +2,6 @@ dist/
 .rumdl_cache/
 .wrangler/
 .astro/
-# css files are linted by biome
-**/*.css
+.nimbus/
 openapi.yaml
 openapi.json

AGENTS.md

@@ -2,20 +2,21 @@
 
 ## Project Structure & Organization
 
-The portal uses Astro with the Starlight theme. Application source sits in `src/`, with `pages/` for route entry points, `content/` for MDX docs, `components/` for reusable UI (React, Astro, and Circuit UI), and `utils/`/`lib/` for shared logic. Assets live in `src/assets` and `public/`. Build outputs go to `dist/`. Configuration resides in `astro.config.ts`, `ec.config.mjs`, and `wrangler.jsonc`; adjust them when adding new content types or deployment targets. API documentation is based on `openapi.yaml`, this file is synchronized from outside this repository, do not edit it.
+The portal uses Astro with Nimbus. Application source sits in `src/`, with `pages/` for route entry points, `content/` for MDX docs, `layouts/` and `components/` for repository-owned UI (React, Astro, and Circuit UI), and `utils/`/`lib/` for shared logic. Assets live in `src/assets` and `public/`. Build outputs go to `dist/`. Configuration resides in `astro.config.ts`, `nimbus.json`, and `wrangler.jsonc`; adjust them when adding new content types or deployment targets. API documentation is based on `openapi.yaml`, this file is synchronized from outside this repository, do not edit it.
 
 ## Build, Test, and Development Commands
 
 - `npm run dev` — watch mode with Hot Module Reloading; use when authoring docs or components.
 - `npm run build` — production Astro build targeting Cloudflare; ensure it succeeds before merging.
-- `npm run check` — runs `astro check` for type and content schema validation after `astro sync`.
-- `npm run lint` — ESLint across Astro/TSX files; required before pushing structural changes.
-- `npm run format` — Prettier write for source and content; run after bulk edits.
-- `npm run linkcheck` — builds with `CHECK_LINKS=true` to surface broken internal/external links.
+- `npm run check` — runs `astro check` for Astro, TypeScript, and content schema validation.
+- `npm run lint` — runs ESLint and `rumdl`; required before pushing structural changes.
+- `npm run format` — formats source, styles, and data files with Prettier.
+- `npm run linkcheck` — builds, runs Nimbus's internal-link checks, and validates rendered API links.
+- `npm run validate` — runs the complete CI validation sequence.
 
 ## Coding Style & Naming Conventions
 
-Prettier (project defaults) handles whitespace, so commit formatted files rather than manual styling. Stick to TypeScript where possible; Astro islands may embed React components. Name components and directories in PascalCase (`src/components/LogoSlider`), utility modules in camelCase (`src/utils/formats.ts`), and content files in kebab-case (`src/content/docs/payments-overview.mdx`). Favor SumUp design tokens and Circuit UI primitives; extend `src/base.css` sparingly.
+Prettier (project defaults) handles whitespace, so commit formatted files rather than manual styling. Stick to TypeScript where possible; Astro islands may embed React components. Name components and directories in PascalCase (`src/components/LogoSlider`), utility modules in camelCase (`src/utils/formats.ts`), and content files in kebab-case (`src/content/docs/payments-overview.mdx`). Favor SumUp design tokens and Circuit UI primitives; extend `src/styles/portal.css` and `src/styles/prose.css` sparingly. Do not add Tailwind.
 
 ## Docs Frontmatter Requirements
 
@@ -40,7 +41,7 @@ For files in `src/content/docs/`, include frontmatter at the top of every page.
 
 ## Testing Guidelines
 
-CI relies on `npm run check`. When editing MDX content, preview via `npm run dev` to verify navigation, sidebar ordering, and snippet rendering. There is no Jest-style test suite; document any manual verification steps in the pull request if behavior changes or APIs are added.
+CI runs `npm run validate`. When editing MDX content, preview via `npm run dev` to verify navigation, sidebar ordering, and snippet rendering. The repository has a focused Vitest suite for runtime helpers; document any additional manual verification steps in the pull request when UI behavior changes.
 
 ## Markdown Linting Guidelines
 

CONTRIBUTING.md

@@ -1,7 +1,7 @@
 # Contributing
 
-SumUp Developer portal built using [Starlight](https://starlight.astro.build/), a documentation theme built on top of [Astro](https://astro.build/). Our theme is modified to rely on SumUp's design system - [Circuit UI](https://github.com/sumup-oss/circuit-ui) - wherever possible.
+SumUp Developer portal is built with [Nimbus](https://nimbus-docs.com/), a documentation framework for [Astro](https://astro.build/). The repository owns its visible components and plain CSS, using SumUp's [Circuit UI](https://github.com/sumup-oss/circuit-ui) design system wherever possible. Tailwind is not used.
 
 ## Codeblocks
 
-Codeblocks are rendered using [Expressive Code](https://expressive-code.com/), the configuration can be found in `./ec.config.mjs`.
+Code blocks are highlighted by Nimbus's Shiki pipeline. Site-wide docs behavior is configured in `astro.config.ts`; visible layouts and styles live in `src/layouts/`, `src/components/nimbus/`, and `src/styles/`.

README.md

@@ -7,7 +7,7 @@
 [![License](https://img.shields.io/github/license/sumup/sumup-developer)](./LICENSE)
 [![Contributor Covenant](https://img.shields.io/badge/Contributor%20Covenant-v2.1%20adopted-ff69b4.svg)](https://github.com/sumup/sumup-developer/tree/main/CODE_OF_CONDUCT.md)
 
-The SumUp Developer Portal documents the integrations, SDKs, and public APIs that external developers use to build payment-acceptance solutions. The site is built with [Astro](https://astro.build/) and the [Starlight](https://starlight.astro.build/) documentation theme. Documentation pages are written in Markdown and MDX.
+The SumUp Developer Portal documents the integrations, SDKs, and public APIs that external developers use to build payment-acceptance solutions. The site is built with [Astro](https://astro.build/) and [Nimbus](https://nimbus-docs.com/). Documentation pages are written in Markdown and MDX, while the visible theme uses plain CSS and SumUp's Circuit UI design tokens.
 
 </div>
 
@@ -63,6 +63,7 @@ Run the checks that match your change before opening a pull request:
 | `npm run test` | Run the Vitest test suite |
 | `npm run build` | Create the production Cloudflare build |
 | `npm run linkcheck` | Build the site and validate internal links |
+| `npm run validate` | Run the complete CI validation sequence |
 
 ## API Specs