Error: Stub out support for theming

[noisysocks]

Asana Task/Github Issue: https://app.asana.com/1/137249556945/project/1209121419454298/task/1211842297547581

• Updates the error special page (errorpage) to accept $THEME_VARIANT$ as an interpolated string and expose window.onChangeTheme({ themeVariant }) as a method native can use to adjust the variant in realtime.

• Adjusts the default background colour according to the set variant so that something observable happens when setting a theme.

Intention here is to do the minimal amount needed to unblock the native apps. In follow up PRs I’ll import theme variables from the design-tokens repo and update more than just the background colour.

Testing Steps

1. Browse to https://deploy-preview-2077--content-scope-scripts.netlify.app/build/pages/errorpage/.
2. Check that background colour is light grey (as before).
3. Switch theme to dark using System Settings.
4. Check that background colour is dark grey (as before).
5. Manually modify data-theme-variant to ”rose” (or any valid variant).
6. Check that background colour is pink (or whatever).
7. Switch theme to dark using System Settings.
8. Check that background colour is purple (or whatever).
9. Run window.onChangeTheme({ themeVariant: ‘desert’ }) (or any valid variant) in DevTools.
10. Check that background colour is pink (or whatever).
11. Switch theme to dark using System Settings.
12. Check that background colour is purple (or whatever).

Checklist

<!—
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Please tick all that apply:

• I have tested this change locally
• I have tested this change locally in all supported browsers
• This change will be visible to users
• I have added automated tests that cover this change
• I have ensured the change is gated by config
• This change was covered by a ship review
• This change was covered by a tech design
• Any dependent config has been merged

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Note

Adds theme variant support to the error page via data-theme-variant, a window.onChangeTheme runtime hook, and variant-specific backgrounds for light/dark modes.

• Theming support for pages/errorpage
  • HTML (public/index.html): Initialize body with data-theme-variant="$THEME_VARIANT$"; add window.onChangeTheme(payload) to update document.body.dataset.themeVariant at runtime.
  • CSS (public/style.css): Define background colors for theme variants (coolGray, slateBlue, green, violet, rose, orange, desert) in light and dark modes via [data-theme-variant="..."] selectors.
  • Docs (readme.md): Document theming mechanisms, supported variants, payload format, and example usage.

^{Written by Cursor Bugbot for commit 956e168. This will update automatically on new commits. Configure here.}

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[github-actions]

Temporary Branch Update

The temporary branch has been updated with the latest changes. Below are the details:

• Branch Name: pr-releases/pr-2077
• Commit Hash: 0a78cb7a97e28ce2578ba28deba590e5bb399849
• Last Updated: December 4, 2025 at 9:00:41 AM UTC
• Install Command: npm i github:duckduckgo/content-scope-scripts#0a78cb7a97e28ce2578ba28deba590e5bb399849

Please use the above install command to update to the latest version.

[github-actions]

[Beta] Generated file diff

Time updated: Thu, 04 Dec 2025 09:01:30 GMT

Apple

    - apple/pages/errorpage/index.html

• apple/pages/errorpage/style.css

File has changed

Integration

    - integration/pages/errorpage/index.html

• integration/pages/errorpage/style.css

File has changed