What problem does it solve? Building interfaces that adapt cleanly across phones, tablets, and desktops often leads to brittle breakpoint hacks, fixed pixel widths, and components that break when reused in different contexts. This Skill provides proven patterns for modern responsive CSS so layouts adapt to both viewport and container size. ## Core Features & Use Cases - Container Queries: Build component-level responsiveness with container-type, named containers, and container query units (cqi, cqw) so components adapt wherever they are placed. - Fluid Typography & Spacing: Create smooth-scaling type and spacing scales with CSS clamp(), min(), and max() instead of hard breakpoint jumps. - Responsive Layout Patterns: Apply CSS Grid auto-fit layouts, Flexbox switchers, responsive navigation, tables, and images with srcset and art direction. - Use Case: A card component must show a stacked layout in a narrow sidebar but a horizontal layout in the main content area. Use container queries so the card responds to its own width rather than the viewport. ## Quick Start Ask the AI to refactor a card component to use container queries and fluid typography so it adapts to its container width instead of the viewport.