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Frontend design

Skill s-hiraoku/synapse-a2a/.agents/skills/frontend-design

Guide for creating distinctive, production-grade frontend interfaces. Covers visual design systems, typography, color, motion, spatial composition, and web interface standards. Use when designing UI, establishing design systems, or reviewing visual quality of frontend code.From its SKILL.md

Install
npx -y skills add s-hiraoku/synapse-a2a --skill frontend-design

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SKILL.md

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Frontend Design

Create interfaces with intentional aesthetics and professional execution. Avoid generic "template" looks.

Design Process

Before writing code, answer these questions:

  1. Purpose — What problem does this interface solve? Who uses it?
  2. Tone — What aesthetic direction? (brutalist, luxury, playful, editorial, retro-futuristic, etc.)
  3. Constraints — Device targets, accessibility requirements, performance budget
  4. Signature — What single element makes this memorable?

Commit to a direction. Timid design is worse than bold design with flaws.

Typography

Font Selection

Avoid overused defaults. Choose typefaces that reinforce the interface's personality.

/* BAD: Generic, seen everywhere */
font-family: 'Inter', 'Roboto', 'Arial', sans-serif;

/* GOOD: Distinctive and paired intentionally */
--font-display: 'Instrument Serif', serif;      /* headings */
--font-body: 'Satoshi', sans-serif;              /* body text */
--font-mono: 'Berkeley Mono', monospace;         /* code */

Typographic Details

/* Tabular numbers for aligned columns */
.data-cell { font-variant-numeric: tabular-nums; }

/* Balanced headings prevent widow words */
h1, h2, h3 { text-wrap: balance; }

/* Proper ellipsis character */
.truncate::after { content: '\2026'; } /* … not ... */

Handle text overflow deliberately:

/* Single line truncation */
.truncate { overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }

/* Multi-line clamping */
.clamp-3 { display: -webkit-box; -webkit-line-clamp: 3; -webkit-box-orient: vertical; overflow: hidden; }

/* Flex children need min-w-0 for truncation to work */
.flex-child { min-width: 0; }

Color Systems

Theme Architecture

Build on CSS custom properties with clear semantic naming.

:root {
  /* Primitives */
  --gray-50: oklch(0.98 0.005 240);
  --gray-900: oklch(0.15 0.01 240);
  --accent: oklch(0.65 0.25 30);

  /* Semantic tokens */
  --color-bg: var(--gray-50);
  --color-text: var(--gray-900);
  --color-text-muted: oklch(0.55 0.01 240);
  --color-border: oklch(0.88 0.005 240);
  --color-accent: var(--accent);
  --color-accent-hover: oklch(0.58 0.28 30);
}

@media (prefers-color-scheme: dark) {
  :root {
    --color-bg: var(--gray-900);
    --color-text: var(--gray-50);
    --color-text-muted: oklch(0.65 0.01 240);
    --color-border: oklch(0.28 0.005 240);
  }
}

Color Principles

  • Commit to a palette — 1 dominant + 1–2 accents. Avoid 5-color rainbows.
  • Use oklch — Perceptually uniform, better than hex/hsl for programmatic palettes.
  • Contrast ratios — 4.5:1 minimum for body text, 3:1 for large text (WCAG AA).

Motion & Animation

Rules

  1. Respect user preference: Always honor prefers-reduced-motion
  2. Animate only transform and opacity: These are GPU-composited, everything else triggers layout/paint
  3. Never use transition: all: List specific properties
  4. Animations must be interruptible: User actions should cancel running animations
/* GOOD: Specific properties, respects user preference */
.card {
  transition: transform 200ms ease-out, opacity 150ms ease-out;
}

@media (prefers-reduced-motion: reduce) {
  .card { transition: none; }
}

High-Impact Moments

Focus animation budget on:

  • Page transitions — Orchestrated staggered reveals
  • State changes — Loading → content, collapsed → expanded
  • Feedback — Button press, form submission confirmation

Skip: random hover effects on every element, scroll-jacking, decorative background animations.

Spatial Composition

Layout Principles

  • Asymmetry is interesting — Perfectly centered grid layouts are predictable
  • Intentional negative space — White space is a design element, not a mistake
  • Grid-breaking elements — One element that overlaps or extends beyond the grid creates focus
  • Diagonal flow — Eye movement along diagonals is more engaging than horizontal scan

Responsive Strategy

/* Fluid typography */
h1 { font-size: clamp(2rem, 5vw, 4rem); }

/* Container queries for component-level responsiveness */
.card-container { container-type: inline-size; }

@container (min-width: 400px) {
  .card { grid-template-columns: 200px 1fr; }
}

Backgrounds & Atmosphere

Build visual depth through layered treatments:

/* Noise texture overlay */
.surface::after {
  content: '';
  position: absolute;
  inset: 0;
  background: url('/noise.svg');
  opacity: 0.03;
  pointer-events: none;
}

/* Gradient mesh */
.hero {
  background:
    radial-gradient(ellipse at 20% 50%, oklch(0.7 0.15 250 / 0.3), transparent 50%),
    radial-gradient(ellipse at 80% 20%, oklch(0.7 0.2 30 / 0.2), transparent 50%),
    var(--color-bg);
}

Images & Media

// Explicit dimensions prevent layout shift
<Image src={src} width={800} height={600} alt="Description" />

// Below-fold: lazy load
<Image src={src} loading="lazy" alt="..." />

// Above-fold: prioritize
<Image src={src} priority alt="..." />

// Decorative: empty alt
<Image src={pattern} alt="" aria-hidden="true" />

Interactive States

Every interactive element needs 4 states:

StateTreatment
DefaultBase appearance
HoverIncreased contrast or subtle shift
FocusVisible ring via :focus-visible
Active/PressedSlight scale or color change
DisabledReduced opacity + cursor: not-allowed
.button {
  background: var(--color-accent);
  transition: background 150ms ease-out, transform 100ms ease-out;
}
.button:hover { background: var(--color-accent-hover); }
.button:focus-visible { outline: 2px solid var(--color-accent); outline-offset: 2px; }
.button:active { transform: scale(0.98); }

Anti-Patterns

AvoidInstead
Inter/Roboto/Arial everywhereChoose distinctive, project-appropriate typefaces
Purple gradient on whiteCommit to a specific, cohesive palette
Uniform card gridsVary sizes, add featured/hero cards
Shadows on everythingUse shadow purposefully for elevation hierarchy
border-radius: 9999px on all elementsMatch radius to content type and context
Identical hover effectsTailor interaction feedback to element function

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