- Added 'concept' objects to all 5 Tailwind lessons explaining utility-first approach
- Lesson 1 (Backgrounds): Explains pre-built utilities vs custom CSS, color scale system
- Lesson 2 (Utility-First): Explains utility-first philosophy and problems it solves
- Lesson 3 (Text Utilities): Explains naming patterns and color shade system
- Lesson 4 (Spacing): Explains base-4 spacing scale and directional shorthands
- Lesson 5 (Breakpoints): Explains mobile-first responsive utilities and media queries
- All concepts include beginner-friendly explanations and detailed ASCII diagrams
- Emphasizes how Tailwind differs from traditional CSS (no naming, no context-switching, no specificity wars)
- Diagrams show workflow comparisons, naming patterns, spacing scales, and breakpoint cascades
- Replace single quotes with <kbd> tags in validation messages
- German and English lessons updated for consistent formatting
- Move task instruction before description in UI (index.html)
