Improve demo page accessibility and remove code inconsistencies

[coderabbitai]

Based on CodeRabbit review in PR #11: #11

UI/UX Improvements:

1. Accessibility Issues (demo/index.html)

• Add proper ARIA labels for stack direction button group
• Remove inline styles, move to CSS classes
• Use semantic HTML for better screen reader support

2. CSS Cleanup (demo/css/styles.css)

• Remove duplicate properties in .demo-header (box-shadow, border-radius)
• Consolidate theme toggle button styles
• Impact: Cleaner CSS, better maintainability

3. JavaScript Improvements (demo/js/script.js)

• Remove empty no-op block in initAllonsh()
• Use declared constants instead of hardcoded class strings
• Consider using resetAll() method for cleaner reset logic

Priority: Low

These improvements enhance user experience and code maintainability.