Add conceptual explanations to all 4 lessons in 05-units-variables.json:
- Lesson 1 (Absolute vs Relative Units): Explains fixed px vs scalable rem/%, why rem is preferred for accessibility, and how units calculate
- Lesson 2 (CSS Custom Properties): Explains variable definition/reference, inheritance cascade, scoping, and live updates vs preprocessor variables
- Lesson 3 (calc): Explains runtime calculation, mixing units, syntax requirements for operators
- Lesson 4 (Viewport Units): Explains vw/vh/vmin/vmax relative to viewport, auto-resize behavior, and difference from percentage units
All concepts include beginner-friendly explanations (2-4 sentences) and detailed ASCII diagrams showing calculations and visual representations.
- Hello World lesson now styles plain text (no h1 required)
- Added syntax examples to CSS Variables, calc(), Media Queries, Flexbox, Grid
- Added goodbye/offboarding module with contribution encouragement
- Add contact section to help dialog with librete.ch, GitHub, Gitea, LinkedIn links
- Add HTML/CSS prefixes to English module titles for consistency with German
- Add CSS transitions for smooth lesson switching
- Add transitioning class to prevent content flash during lesson changes
- Add <kbd> tags to CSS property values and selectors in task descriptions
- Add solution code to all lessons for better guidance
- Improve animation contrast in transitions lesson (black/white instead
of similar purples, dramatic color changes for visibility)
- Simplify validation messages with kbd formatting
