Update progress tracking for subtask 2.2 completion

.auto-claude/specs/001-conceptual-explanations/build-progress.txt

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+# Build Progress: Conceptual Explanations Feature
+
+## Overview
+Adding "Why This Works" explanations to each lesson that explain the concept behind CSS properties, not just syntax.
+
+## Status: Planning Complete
+
+### Implementation Plan Created: 2025-01-11
+
+**6 Phases with 20 Subtasks:**
+
+1. **Schema & Data Model** (1 subtask)
+   - Update lesson JSON schema with concept field
+
+2. **UI Components** (4 subtasks)
+   - Add collapsible concept section to HTML
+   - Style the concept section
+   - Update renderer to display concepts
+   - Add i18n keys for concept UI
+
+3. **Content - Core CSS Modules** (5 subtasks)
+   - Flexbox lessons (with container vs item distinction)
+   - Grid lessons
+   - Basic selectors
+   - Box model
+   - Advanced selectors
+
+4. **Content - Visual & Layout Modules** (6 subtasks)
+   - Colors, Typography, Units/Variables
+   - Transitions/Animations, Layouts, Responsive
+
+5. **Content - HTML & Tailwind Modules** (4 subtasks)
+   - HTML elements, Forms, Advanced HTML elements
+   - Tailwind basics
+
+6. **Testing & Polish** (3 subtasks)
+   - Unit tests, Mobile responsiveness, Final review
+
+---
+
+## Codebase Analysis
+
+### Key Files:
+- schemas/code-crispies-module-schema.json - Lesson schema definition
+- src/index.html - Main HTML layout
+- src/main.css - Styles
+- src/helpers/renderer.js - Lesson rendering
+- src/i18n.js - Internationalization
+- lessons/*.json - ~30 lesson modules (EN), with translations
+
+### Current Lesson Structure:
+- Lessons have: id, title, description, task, previewHTML, validations
+- No "concept" field exists yet
+- Description field is used for general info, not conceptual explanations
+
+### UI Pattern:
+- Uses native HTML5 elements (dialog, details/summary elsewhere)
+- Left panel: instructions + editor
+- Right panel: preview + navigation
+
+---
+
+## Next Steps
+Ready to begin Phase 1: Schema & Data Model
+
+[2025-01-11 - Subtask 1.1 COMPLETED]
+✓ Added 'concept' object field to lesson schema (code-crispies-module-schema.json)
+✓ Schema properties:
+  - explanation: required string for 2-4 sentence beginner-friendly explanation
+  - diagram: optional string for SVG/ASCII art visualizations
+  - containerVsItem: optional string for Flexbox/Grid container vs item distinction
+✓ Schema validated successfully
+✓ Committed changes: 4486078
+
+
+=== 2026-01-11 - Subtask 2.1 Completed ===
+Added native <details><summary> element for 'Why This Works' section.
+
+Implementation details:
+- Added concept section in src/index.html within .instructions section (lines 37-44)
+- Used semantic HTML5 <details> element for native collapsible behavior
+- Included <summary> with data-i18n="whyThisWorks" for internationalization
+- Created three content divs: concept-explanation, concept-diagram, concept-container-vs-item
+- Maintained proper indentation and tab formatting
+- Follows accessibility best practices with semantic HTML
+
+Committed: 2a9565c
+Status: ✓ Completed
+
+
+=== 2026-01-11 - Subtask 2.2 Completed ===
+Added CSS styles for the concept panel with distinct visual treatment and smooth animations.
+
+Implementation details:
+- Added comprehensive CSS styles for all concept section elements in src/main.css
+- Distinct visual treatment:
+  * Light purple background (var(--primary-bg-light))
+  * 3px left border in primary color for visual emphasis
+  * Hover effects changing background to var(--primary-bg-medium)
+  * Open state styling for active disclosure
+- Smooth animations:
+  * Rotating arrow icon (▶ to ▼) with 0.2s transition
+  * Fade-in and slide-down animation (concept-expand keyframes)
+  * Background color transitions on hover
+- Diagram container styling:
+  * White background with border and padding
+  * Monospace font for code/diagrams
+  * Overflow-x handling for wide diagrams
+  * Auto-hide when empty using :empty pseudo-class
+- Special container-vs-item section:
+  * Success color theming (green background and border)
+  * Distinct styling to highlight Flexbox/Grid distinctions
+- RTL support:
+  * Border positions flip for right-to-left languages
+  * Flex direction reversal for proper layout
+- CSS variables used throughout for consistency:
+  * --spacing-* for all spacing
+  * --primary-*, --success-* for colors
+  * --border-radius-* for border radii
+  * --font-code for monospace text
+- Follows all existing codebase patterns and design system
+
+Committed: 0e39cff
+Status: ✓ Completed