Skill — Responsive Patterns

When this skill activates

Any task involving responsive layout architecture, mobile-first design, adaptive components, fluid sizing, or multi-viewport support.

Mandatory actions when this skill is active

Before writing any code

1. Determine if the design is mobile-first or desktop-first (prefer mobile-first).
2. Identify content-based breakpoints (where the layout breaks, not device widths).
3. Decide between page-level media queries vs component-level container queries.

During implementation

• Use min-width media queries for mobile-first progressive enhancement.
• Apply container queries for reusable components that adapt to their parent.
• Use fluid typography with clamp() for smooth scaling without breakpoints.
• Prefer CSS Grid for 2D layouts, Flexbox for 1D alignment.
• Use modern viewport units (dvh, svw, lvw) for mobile Safari compatibility.

After implementation

• Test at minimum: 320px, 768px, 1024px, 1440px viewports.
• Verify no horizontal scroll at any viewport width.
• Check touch targets are minimum 44x44px on mobile.
• Validate images load appropriate sizes (not desktop images on mobile).

Core strategies

Mobile-First

/* Base styles (mobile) */
.card { padding: 1rem; }

/* Tablet and up */
@media (min-width: 48rem) {
  .card { padding: 1.5rem; }
}

/* Desktop and up */
@media (min-width: 64rem) {
  .card { padding: 2rem; }
}

Container Queries

.card-container { container-type: inline-size; }

@container (min-width: 400px) {
  .card { display: grid; grid-template-columns: 1fr 2fr; }
}

@container (min-width: 700px) {
  .card { grid-template-columns: 1fr 3fr 1fr; }
}

Fluid Typography

/* Scales from 1rem at 320px to 2rem at 1200px */
h1 { font-size: clamp(1rem, 0.5rem + 2.5vw, 2rem); }

/* Body text with subtle scaling */
body { font-size: clamp(0.875rem, 0.8rem + 0.25vw, 1rem); }

Breakpoint Strategy

• Do NOT use device-based breakpoints (iPhone, iPad, etc.).
• Add a breakpoint when content breaks or becomes unreadable.
• Common content breakpoints: ~30rem, ~48rem, ~64rem, ~80rem.
• Name tokens semantically: --bp-compact, --bp-medium, --bp-wide.

CSS Grid Layouts

/* Auto-fit responsive grid — no media queries needed */
.grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(100%, 300px), 1fr));
  gap: 1.5rem;
}

Responsive Images

<!-- srcset for resolution switching -->
<img
  srcset="image-400.webp 400w, image-800.webp 800w, image-1200.webp 1200w"
  sizes="(max-width: 48rem) 100vw, (max-width: 64rem) 50vw, 33vw"
  src="image-800.webp"
  alt="Description"
  loading="lazy"
/>

<!-- picture for art direction -->
<picture>
  <source media="(min-width: 64rem)" srcset="wide.webp" />
  <source media="(min-width: 48rem)" srcset="medium.webp" />
  <img src="narrow.webp" alt="Description" />
</picture>

Viewport Units

/* Use dvh for mobile Safari (accounts for address bar) */
.hero { min-height: 100dvh; }

/* svh = smallest viewport height (address bar visible) */
.sticky-footer { height: 100svh; }

Adaptive Components (Slot-Based)

Design components that render different internal layouts based on container size:

• Compact: stacked layout, icon-only buttons.
• Medium: side-by-side layout, abbreviated labels.
• Wide: full layout, expanded content, additional metadata.

Anti-patterns to avoid

• Fixed pixel widths on containers (use max-width + percentage/auto).
• Device-specific breakpoints (will break on next year's devices).
• Hiding content with display: none at breakpoints (serve less content instead).
• Using vw for font-size without clamp() (too small on mobile, too large on 4K).
• Horizontal scrolling caused by fixed-width elements or overflow.

Self-check before task completion

Before marking a task done when this skill was active:

• [ ] Layout works at 320px without horizontal scroll?
• [ ] Typography scales fluidly without jarring jumps?
• [ ] Images serve appropriate sizes per viewport?
• [ ] Touch targets are 44x44px minimum on mobile?
• [ ] Container queries used for reusable component responsiveness?
• [ ] No device-specific breakpoints in the code?