added dark mode theme

[amreshanand]

📝 Description

This pull request introduces dark theme support for the Permission Site project.
The goal is to improve accessibility and provide a better visual experience for users who prefer dark mode.

🔧 Changes Made

Implemented a dark color palette (background, text, and button styles).

Updated CSS variables for theme switching.

Added toggle button for light/dark mode.

Ensured contrast ratios meet accessibility standards.

Verified consistent layout and responsive design across pages.

🧪 Testing

Manually tested in Chrome, Firefox, and Safari.

Verified that both light and dark themes display correctly.

Checked that theme preference persists across sessions (using local storage).

🧭 Additional Notes

No breaking changes introduced.

Code follows existing project style and naming conventions.

Ready for review and feedback.

✅ Checklist

Code compiles without errors

All existing tests pass.

UI verified for consistency.y

Follow the style guidelines

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