phsl / new-api

This commit improves the codebase structure by:
- Moving all inline styles from SiderBar.js to CSS classes in index.css
- Organizing CSS with clear section comments for better maintainability
- Removing unused imports and components
- Improving sidebar design with cleaner styling and consistent color management
- Restructuring CSS to group related styles together
- Adjusting sidebar width from 200px to 180px
- Replacing Text components with semantic divs for group labels
- Creating a color management function for sidebar icons