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Feature: Theme Toggle

Purpose​

  • Feature name: Theme toggle
  • Why this feature exists: Allow reviewers to switch between light and dark themes while preserving accessibility.

Scope​

In scope​

  • theme toggle UI and interaction
  • persistence in local storage
  • system preference fallback

Out of scope​

  • CSS variable definitions (covered in theme system)
  • scroll animations (covered in navigation and UX polish)

Prereqs / Inputs​

  • client-side JavaScript enabled
  • prefers-color-scheme available in browser

Procedure / Content​

Feature summary​

  • Feature name: Theme toggle
  • Feature group: Theming and accessibility
  • Technical summary: Toggles the dark class on the root element and persists the setting in local storage.
  • Low-tech summary: A button that switches the site between light and dark modes.

Feature in action​

  • Where to see it working: Header on any route, such as / or /projects.

Confirmation Process​

Manual​

  • Steps: Toggle the theme, refresh the page, and verify the preference persists.
  • What to look for: Theme changes immediately, persists across reloads, and respects system preference on first load.
  • Artifacts or reports to inspect: None.

Tests​

Potential behavior if broken or misconfigured​

  • Theme does not persist after reload.
  • Theme toggle causes hydration mismatch warnings.

Long-term maintenance notes​

  • Re-test after changes to layout or theme initialization scripts.

Dependencies, libraries, tools​

  • Next.js App Router
  • React
  • Tailwind CSS

Source code references (GitHub URLs)​

ADRs​

Runbooks​

  • None.

Additional internal references​

Validation / Expected outcomes​

  • Theme toggle changes appearance immediately and persists across reloads.

Failure modes / Troubleshooting​

  • Theme does not persist: verify local storage usage.
  • Flash of wrong theme: validate pre-hydration script.

References​

  • None.