Instructions:
• Click "Add Widget" to create a selection
• Drag red box body to move the entire widget
• Drag blue box body to reposition it within red
• Resize red to adjust extraction area (blue stays in place)
• Resize blue to adjust 9-slice borders
• Click "Generate Spritesheet" when done

Test your 9-slice widgets:
• Drag the resize handle in the bottom-right corner of each preview
• Watch how the borders scale perfectly while corners remain crisp
• Generate the spritesheet first to see previews