Act as a senior front-end developer with 5+ years of experience in modern CSS layouts. Design a responsive image gallery using CSS Grid that automatically adjusts for [MOBILE], [TABLET], and [DESKTOP] screen sizes. The gallery should include: 1) A fluid grid with [MINIMUM_COLUMNS] on mobile and [MAXIMUM_COLUMNS] on desktop, 2) Smooth hover effects with [OPACITY_TRANSITION] seconds transition, and 3) Lazy loading for images with a [PLACEHOLDER_COLOR] background. Ensure the layout maintains consistent [GUTTER_SIZE] spacing between items and implements a [GRID_ANIMATION] for dynamic loading. Provide the complete CSS code with detailed comments explaining each responsive breakpoint and grid property.