Fix flashcards being positioned outside visible area by using the
container's actual dimensions instead of hardcoded pixel values.
The previous implementation used CONTAINER_WIDTH=800px and
CONTAINER_HEIGHT=500px to position cards, but the actual container
width is 100% which varies by screen size. This caused cards to be
positioned outside the visible area on smaller screens.
Changes:
- Add containerRef to get actual container dimensions
- Calculate card positions based on offsetWidth/offsetHeight
- Remove hardcoded dimension constants
- Ensure cards stay within visible bounds with proper margins
This makes the flashcard positioning responsive to any screen size.
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Co-Authored-By: Claude <noreply@anthropic.com>
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