Add night mode (dark mode) toggle feature - Resolves #82

[yush-1018]

This PR adds a night mode (dark mode) toggle feature to the documentation website, resolving issue #82.

Changes Made

• Added a floating toggle button in the bottom-right corner
• Implemented comprehensive dark mode styling for all page elements
• Added localStorage support to persist user's theme preference
• Included smooth animations and transitions
• Created documentation file explaining the implementation

Features

✅ One-click toggle between light and dark modes
✅ Persistent theme preference (survives page reloads)
✅ Floating button with moon/sun icons
✅ Comprehensive dark styling for:

• Background and text colors
• Navigation sidebar
• Code blocks and syntax highlighting
• Tables, links, and headings
• Header bar

Implementation Details

• File Modified: includes/header.html
• New File: NIGHT_MODE_IMPLEMENTATION.md (documentation)
• Technology: Pure CSS + Vanilla JavaScript (no dependencies)
• Browser Support: All modern browsers with localStorage support

Visual Design

• Light Mode: Original theme maintained
• Dark Mode:
  • Background: #1a1a1a
  • Text: #e0e0e0
  • Sidebar: #2d2d2d
  • Accent colors preserved from original theme

Testing

Tested functionality:

• Toggle button appears and functions correctly
• Dark mode applies to all page elements
• Theme preference persists after page reload
• Navigation between pages maintains theme
• Icons change appropriately (moon ↔️ sun)
• Hover animations work smoothly

Similar Implementation

This implementation follows the same pattern as popular documentation sites like Docker docs and GitHub docs.

Fixes #82

[yush-1018]

Hi @kevinrue! 👋

I've implemented the night mode feature similar to Docker docs.

Features:
🌙 Floating toggle button (bottom-right corner)
💾 Persistent theme preference (localStorage)
🎨 Complete dark mode styling
✨ Smooth animations

How it works:

• Moon icon → switch to dark mode
• Sun icon → switch to light mode
• Preference auto-saves and persists

Modified includes/header.html with pure CSS + vanilla JS (no dependencies).

Let me know if you need any changes! 🚀