| name | interface-kit |
| description | Authoritative guide for implementing stunning, accessible, performant UI. Synthesizes
design engineering philosophy, accessibility standards, animation principles, spatial design,
typography, color systems, and component craft into a single actionable reference.
Complements the design-system skill (which covers DESIGN.md spec writing) by covering
the HOW of implementation.
Trigger phrases: "build UI", "create component", "landing page", "make it look good",
"frontend", "design", "polish UI", "implement design", "make it beautiful",
"UI implementation", "component styling", "animation", "accessibility"
|
Interface Kit: Implementation Guide for Exceptional Interfaces
If a DESIGN.md exists at the project root, its tokens and specifications override all defaults in this skill. This skill provides sensible defaults for when no design system exists, and implementation guidance that applies regardless.
For deep dives on any section, see the reference files in this skill's references/ directory.
1. Core Philosophy
Taste is trained, not innate. Study why great interfaces feel right. Deconstruct apps you admire — the spacing, the timing, the weight of a shadow. The gap between "fine" and "exceptional" is built from hundreds of micro-decisions that users feel but never consciously notice.
Unseen details compound. A single rounded corner, a single eased transition, a single well-chosen shadow — none of these matter alone. Together they become "a thousand barely audible voices singing in tune." The cumulative effect is what separates craft from output.
Beauty is leverage. Polish is not vanity. Good defaults, considered typography, and intentional motion are real differentiators. Users trust interfaces that feel cared for. Investors notice. Competitors can't easily replicate taste.
Intentionality over intensity. Both bold maximalism and refined minimalism work — what fails is the absence of a clear point of view. Every visual decision should trace back to a deliberate conceptual direction. If you can't articulate WHY a choice was made, reconsider it.
Choose a direction and execute with precision. Don't hedge between styles. A brutalist page committed fully will always outperform a page that's "a little bit of everything." Commit, then refine.
NEVER produce generic "AI slop" aesthetics. No gratuitous gradients on white backgrounds. No cookie-cutter hero sections with stock illustrations. No safe, forgettable layouts that could belong to any product. Every interface should have a point of view that makes it recognizable.
2. The Priority Stack
When implementing UI, work through these priorities in order. Higher priorities are non-negotiable; lower priorities are polish that compounds quality.
| Priority | Level | What It Means |
|---|
| Accessibility | CRITICAL | Contrast 4.5:1, keyboard nav, ARIA semantics, visible focus rings. Ship nothing that excludes users. |
| Performance | HIGH | WebP/AVIF images, lazy loading below fold, CLS < 0.1, transform-only animations on the compositor thread. |
| Typography | HIGH | Font smoothing, text-wrap balance/pretty, tabular-nums for data, 65ch max line length. |
| Layout & Spatial | HIGH | 4/8px grid, concentric border radius, optical alignment over geometric. |
| Color & Theme | MEDIUM | HSL custom properties, semantic tokens, dark mode pairs tested separately. |
| Motion & Interaction | MEDIUM | Frequency-based animation decisions, 150-300ms durations, ease-out default. |
| Polish & Details | LOW | Layered shadows over borders, press feedback on buttons, staggered enter animations. |
Never skip a CRITICAL/HIGH item to chase a LOW item. A beautifully animated button that fails keyboard navigation is a net negative.
3. Aesthetic Direction
Before writing a single line of CSS, commit to a bold aesthetic direction. The most common failure mode in AI-generated UI is convergence on the same safe, forgettable look.
Pick a Tone
Choose one and commit fully:
- Brutally minimal — generous whitespace, monospace type, stark contrast, near-zero decoration
- Maximalist chaos — layered textures, clashing type scales, dense information, intentional visual noise
- Retro-futuristic — CRT glow effects, monospace terminals, scan lines, neon on dark
- Organic / natural — earth tones, rounded shapes, paper textures, hand-drawn accents
- Luxury / refined — serif headlines, muted palettes, ample negative space, subtle gold or cream accents
- Editorial / magazine — dramatic type hierarchy, full-bleed imagery, grid-breaking layouts
- Playful / bold — bright primaries, chunky borders, exaggerated shadows, bouncy motion
Match Complexity to Vision
Maximalist design demands elaborate code — layered backgrounds, complex grid structures, multiple font stacks. Minimalist design demands surgical precision — every pixel of spacing matters more when there's nothing to hide behind.
The Ban List (When No DESIGN.md Exists)
When building without an existing design system, avoid these overused defaults that signal "AI-generated":
- Fonts: Inter, Roboto, Arial, system-ui as display fonts, Space Grotesk
- Colors: Purple-to-blue gradients on white backgrounds
- Patterns: Generic hero with centered text + CTA + stock illustration
Vary between light and dark themes, different font pairings, different aesthetic directions. Never converge on the same choices across projects.
Visual Texture
Add depth through: gradient meshes, noise/grain overlays (filter: url(#noise)), layered transparencies, subtle background patterns, duotone image treatments.
DESIGN.md overrides this entire section. If DESIGN.md specifies Inter, use Inter. If it specifies purple gradients, use them. The ban list only applies when no design system exists and you're making aesthetic choices from scratch.
4. Typography Essentials
Typography is the single highest-leverage design element. Get it right and mediocre layouts still feel good. Get it wrong and nothing else saves it.
Root Setup
html {
-webkit-font-smoothing: antialiased;
-moz-osx-font-smoothing: grayscale;
text-rendering: optimizeLegibility;
}
Apply font smoothing to the root layout. On macOS, the default sub-pixel rendering makes text appear heavier than the designer intended.
Text Wrapping
h1, h2, h3, h4, h5, h6 {
text-wrap: balance;
}
p, li, dd, blockquote {
text-wrap: pretty;
}
balance distributes heading lines evenly. pretty avoids orphaned words in body text.
Numeric Display
.data-value, .price, .counter, [data-numeric] {
font-variant-numeric: tabular-nums;
}
Use tabular-nums for any number that updates dynamically — prices, counters, table columns. Without it, layout shifts as digit widths change.
Scale and Rhythm
- Base size: 16px minimum for body text. Never go below 14px for any readable content.
- Line height: 1.5-1.75 for body text, 1.1-1.3 for large headings.
- Max line length:
max-width: 65ch for body text. Long lines destroy readability.
- Type scale: Pick a consistent scale and stick to it: 12 / 14 / 16 / 18 / 24 / 32 / 48 / 64.
Font Pairing
Pair a distinctive display font with a refined body font. The display font carries personality; the body font carries readability. Use font-weight for hierarchy within a family:
- Headings: 600-700 (semibold to bold)
- Body: 400 (regular)
- Labels / UI: 500 (medium)
Always include font stack fallbacks:
--font-display: "Instrument Serif", "Georgia", serif;
--font-body: "Söhne", "Helvetica Neue", sans-serif;
--font-mono: "JetBrains Mono", "Fira Code", monospace;
5. Color & Theme
HSL Custom Properties (shadcn Pattern)
:root {
--background: 0 0% 100%;
--foreground: 222.2 84% 4.9%;
--primary: 222.2 47.4% 11.2%;
--primary-foreground: 210 40% 98%;
--secondary: 210 40% 96.1%;
--secondary-foreground: 222.2 47.4% 11.2%;
--muted: 210 40% 96.1%;
--muted-foreground: 215.4 16.3% 46.9%;
--accent: 210 40% 96.1%;
--accent-foreground: 222.2 47.4% 11.2%;
--destructive: 0 84.2% 60.2%;
--destructive-foreground: 210 40% 98%;
--border: 214.3 31.8% 91.4%;
--ring: 222.2 84% 4.9%;
--radius: 0.5rem;
}
Define semantic tokens: primary, secondary, destructive, muted, accent, background, foreground. Reference colors by semantic name — never hardcode hex values in components.
Dark Mode
.dark {
--background: 222.2 84% 4.9%;
--foreground: 210 40% 98%;
}
Dark mode is not "invert colors." Use desaturated, lighter tonal variants. Backgrounds go dark but not pure black (#000). Text goes light but not pure white (#fff). Test contrast separately for dark mode — what passes in light may fail in dark.
Contrast Requirements
- WCAG AA minimum: 4.5:1 for normal text, 3:1 for large text (18px+ bold or 24px+ regular)
- Never convey information by color alone — always pair with an icon, label, or pattern
- Test with browser devtools contrast checker or axe-core
Color Confidence
Dominant colors with sharp accents outperform timid, evenly-distributed palettes. Pick one or two hero colors and let the rest of the palette recede. A confident palette has clear hierarchy; an uncertain palette spreads color evenly and feels flat.
6. Spatial Design
Concentric Border Radius
This is the single most common thing that makes nested UI elements feel "off":
outer_radius = inner_radius + padding
.card { border-radius: 16px; padding: 8px; }
.card-inner { border-radius: 8px; }
.card { border-radius: 12px; }
.card-inner { border-radius: 12px; }
When geometric centering looks off, align optically. Play/pause icons, dropdown carets, and asymmetric glyphs often need 1-2px manual nudges to look centered.
Shadows Over Borders
Layer multiple transparent box-shadow values for natural depth instead of using borders:
.elevated {
box-shadow:
0 1px 2px rgba(0, 0, 0, 0.04),
0 2px 4px rgba(0, 0, 0, 0.04),
0 4px 8px rgba(0, 0, 0, 0.04);
}
Multiple shadows at different spreads mimic how light works. A single hard shadow looks artificial.
Image Outlines
Add a subtle inset outline to images and media for consistent depth against varied backgrounds:
img, video {
outline: 1px solid rgba(0, 0, 0, 0.06);
outline-offset: -1px;
}
Spacing Scale
Use a 4px / 8px base incremental system. Every spacing value should be a multiple of 4:
4 / 8 / 12 / 16 / 24 / 32 / 48 / 64 / 96 / 128
Hit Areas
Minimum 44x44px for all interactive elements. If the visual element is smaller, extend the hit area with a pseudo-element:
.small-button::before {
content: "";
position: absolute;
inset: -8px;
}
Z-Index Scale
Define a layered scale and never use arbitrary values:
--z-base: 0;
--z-dropdown: 10;
--z-sticky: 20;
--z-overlay: 40;
--z-modal: 100;
--z-toast: 1000;
7. Motion & Interaction
The Frequency-Based Decision Framework
This is the most important mental model for animation decisions:
| Frequency | Examples | Animation |
|---|
| 100+ times/day | Keyboard shortcuts, command palette actions, tab switches | None. Zero animation. Instant. |
| Tens of times/day | Hover effects, list item navigation, toggles | Remove or drastically reduce. 50-100ms max. |
| Occasional | Modals, drawers, toasts, page transitions | Standard animation. 150-300ms. |
| Rare / first-time | Onboarding, celebrations, empty states | Can add delight. 300-500ms, more elaborate. |
High-frequency animations feel sluggish. Low-frequency animations without motion feel jarring. Match the animation budget to usage frequency.
Custom Easing Curves
Built-in CSS easings (ease, ease-in-out) are too weak. Define custom curves:
:root {
--ease-out: cubic-bezier(0.23, 1, 0.32, 1);
--ease-in-out: cubic-bezier(0.77, 0, 0.175, 1);
--ease-drawer: cubic-bezier(0.32, 0.72, 0, 1);
--ease-spring: cubic-bezier(0.34, 1.56, 0.64, 1);
}
Duration Guide
| Element | Duration |
|---|
| Buttons, toggles | 100-160ms |
| Tooltips | 125-200ms |
| Dropdowns, popovers | 150-250ms |
| Modals, drawers | 200-500ms |
| Page transitions | 250-400ms |
UI animations should stay under 300ms. Never use ease-in for UI animations — it front-loads the pause and feels sluggish.
Enter/Exit Asymmetry
Exits should be softer and faster than enters. An enter animation at 250ms should have its exit at 150-200ms.
Split and Stagger Enter Animations
When multiple elements enter the viewport, stagger them by semantic chunks with ~50-100ms delay:
.stagger-item {
animation: fadeSlideIn 300ms var(--ease-out) both;
}
.stagger-item:nth-child(1) { animation-delay: 0ms; }
.stagger-item:nth-child(2) { animation-delay: 60ms; }
.stagger-item:nth-child(3) { animation-delay: 120ms; }
Scale Animations
Never animate from scale(0). Start from scale(0.9) or higher, combined with opacity:
@keyframes scaleIn {
from { opacity: 0; transform: scale(0.95); }
to { opacity: 1; transform: scale(1); }
}
Press Feedback
Every pressable element should scale down slightly on :active:
button:active {
transform: scale(0.97);
}
Interruptibility
Use CSS transitions (not keyframe animations) for interactive state changes. Transitions can be interrupted mid-way; keyframes cannot. This matters for hover states, toggles, and any element the user might interact with rapidly.
Popover Origin
Make popovers transform-origin aware — they should grow from their trigger element, not from center. Exception: modals always originate from center.
Tooltip Hover Delay
Skip the tooltip delay on subsequent hovers. If the user has already waited for one tooltip, show the next one immediately.
Reduced Motion
@media (prefers-reduced-motion: reduce) {
*, *::before, *::after {
animation-duration: 0.01ms !important;
transition-duration: 0.01ms !important;
}
}
Respect prefers-reduced-motion. Reduce animations — don't eliminate opacity and color transitions entirely, as those provide important feedback.
Hover Gate
Gate hover animations behind a media query so touch devices don't trigger stuck hover states:
@media (hover: hover) and (pointer: fine) {
.card:hover { transform: translateY(-2px); }
}
Reference references/animation-playbook.md for deep dives on spring physics, gesture-driven animation, and complex choreography.
8. Component Craft
Primitives
Use Radix UI primitives for accessible, unstyled foundations. Use CVA (class-variance-authority) for type-safe component variants:
import { cva } from "class-variance-authority";
const buttonVariants = cva(
"inline-flex items-center justify-center rounded-md font-medium transition-colors focus-visible:outline-none focus-visible:ring-2",
{
variants: {
variant: {
default: "bg-primary text-primary-foreground hover:bg-primary/90",
destructive: "bg-destructive text-destructive-foreground hover:bg-destructive/90",
outline: "border border-input hover:bg-accent hover:text-accent-foreground",
ghost: "hover:bg-accent hover:text-accent-foreground",
},
size: {
sm: "h-9 px-3 text-sm",
default: "h-10 px-4 py-2",
lg: "h-11 px-8 text-lg",
},
},
defaultVariants: { variant: "default", size: "default" },
}
);
Button
- Scale on press (
transform: scale(0.97) on :active)
- Visible focus ring (never
outline: none without replacement)
- Loading state with spinner replacing label, maintaining button dimensions
- Disabled state at
opacity: 0.5 with pointer-events: none
Card
- Concentric border radius between card and inner elements
- Layered shadows (not borders) for depth
- Hover state: subtle elevation change (
translateY(-1px) + shadow increase)
Dialog / Modal
- Focus trap (keyboard cannot escape to elements behind)
- ESC to close, click outside overlay to close
transform-origin: center, fade + scale enter animationaria-modal="true", role="dialog", aria-labelledby
Form
- Visible labels always — never placeholder-only inputs
- Error messages near the field with
aria-live="polite" for screen readers
- Progressive disclosure: show advanced fields only when needed
- Use React Hook Form + Zod for validation
Theming
Use shadcn CSS variable pattern (HSL format) for all component colors. Wrap client-interactive components in server components for Next.js App Router compatibility.
Reference references/component-patterns.md for the full component catalog with copy-paste implementations.
9. Accessibility Essentials
Semantic HTML First
Use <button>, <nav>, <main>, <header>, <footer>, <article>, <section> before reaching for ARIA. A <button> gives you keyboard handling, focus management, and screen reader semantics for free. A <div onClick> gives you none of that.
Keyboard Navigation
- Tab / Shift+Tab: move between focusable elements
- Enter / Space: activate buttons and links
- Arrow keys: navigate within lists, menus, tabs, radio groups
- Escape: close modals, popovers, dropdowns
- Home / End: jump to first/last item in lists
Focus Management
- Visible focus rings on all interactive elements — NEVER use
outline: none without a replacement
- Trap focus inside modals (Tab wraps within the modal, not behind it)
- Restore focus to the trigger element when a modal/popover closes
- Use
focus-visible to show rings only for keyboard users, not mouse clicks:
:focus-visible {
outline: 2px solid var(--ring);
outline-offset: 2px;
}
ARIA Attributes
aria-label for icon-only buttons: <button aria-label="Close menu">X</button>aria-labelledby to associate headings with sectionsaria-describedby to link help text or error messages to inputsaria-live="polite" for dynamic content updates (toast messages, form errors)aria-hidden="true" for decorative elements (icons next to text labels)aria-expanded for toggleable elements (dropdowns, accordions)
Color and Contrast
- WCAG AA: 4.5:1 for normal text, 3:1 for large text
- Never use color as the sole indicator — pair with icons, text, or patterns
- Test in both light and dark modes
Images and Media
- Descriptive
alt text for meaningful images: alt="Dashboard showing 23% revenue growth"
- Empty
alt="" for purely decorative images
- Captions for video, transcripts for audio
Navigation Aids
- Skip link: first focusable element, hidden until focused:
<a href="#main-content" class="sr-only focus:not-sr-only">
Skip to main content
</a>
- Heading hierarchy: sequential h1 through h6, no level skips. One
<h1> per page.
Touch Targets
- Minimum 44x44px interactive area
- 8px minimum spacing between adjacent touch targets
- Extend small visual elements with invisible padding or pseudo-elements
Testing
- Automated: axe-core in CI, Lighthouse accessibility score 90+
- Manual: full keyboard-only navigation test
- Screen reader: test with VoiceOver (macOS) or NVDA (Windows)
- Visual: zoom to 200%, check nothing breaks or overlaps
Reference references/accessibility-checklist.md for the full audit guide with pass/fail criteria.
10. Pre-Delivery Review
Run through this checklist before considering any UI implementation complete:
Typography
Color
Spatial
Motion
Accessibility
Reference references/review-checklist.md for the extended 30-item checklist with severity ratings and automated testing commands.
