name: ui-design-system
description: Complete design system with principles + living style guide. Enforces precise, crafted UI inspired by Linear, Notion, and Stripe. Includes boilerplate style-guide page template for Next.js/React projects. Use when building any UI that needs Jony Ive-level precision.

Design System

This skill provides a complete design system: the philosophy (how to think about design) and the documentation (a living style guide template). Every interface should look designed by a team that obsesses over 1-pixel differences.

Workflow

1. Start with Design Direction — Read Part 1 and commit to a direction before writing code
2. Apply Craft Principles — Follow the core rules in Part 2 as you build
3. Document in Style Guide — Add every component to the style guide (Part 3)

Part 1: Design Direction

Before writing any code, commit to a design direction. Don't default. Think about what this specific product needs to feel like.

Think About Context

• What does this product do? A finance tool needs different energy than a creative tool.
• Who uses it? Power users want density. Occasional users want guidance.
• What's the emotional job? Trust? Efficiency? Delight? Focus?
• What would make this memorable? Every product has a chance to feel distinctive.

Choose a Personality

Enterprise/SaaS UI has more range than you think. Consider these directions:

Precision & Density — Tight spacing, monochrome, information-forward. For power users who live in the tool. Think Linear, Raycast, terminal aesthetics.

Warmth & Approachability — Generous spacing, soft shadows, friendly colors. For products that want to feel human. Think Notion, Coda, collaborative tools.

Sophistication & Trust — Cool tones, layered depth, financial gravitas. For products handling money or sensitive data. Think Stripe, Mercury, enterprise B2B.

Boldness & Clarity — High contrast, dramatic negative space, confident typography. For products that want to feel modern and decisive. Think Vercel, minimal dashboards.

Utility & Function — Muted palette, functional density, clear hierarchy. For products where the work matters more than the chrome. Think GitHub, developer tools.

Data & Analysis — Chart-optimized, technical but accessible, numbers as first-class citizens. For analytics, metrics, business intelligence.

Pick one. Or blend two. But commit to a direction that fits the product.

Choose a Color Foundation

Don't default to warm neutrals. Consider the product:

• Warm foundations (creams, warm grays) — approachable, comfortable, human
• Cool foundations (slate, blue-gray) — professional, trustworthy, serious
• Pure neutrals (true grays, black/white) — minimal, bold, technical
• Tinted foundations (slight color cast) — distinctive, memorable, branded

Light or dark? Dark modes aren't just light modes inverted. Dark feels technical, focused, premium. Light feels open, approachable, clean. Choose based on context.

Accent color — Pick ONE that means something. Blue for trust. Green for growth. Orange for energy. Violet for creativity. Don't just reach for the same accent every time.

Choose a Layout Approach

The content should drive the layout:

• Dense grids for information-heavy interfaces where users scan and compare
• Generous spacing for focused tasks where users need to concentrate
• Sidebar navigation for multi-section apps with many destinations
• Top navigation for simpler tools with fewer sections
• Split panels for list-detail patterns where context matters

Choose Typography

Typography sets tone. Don't always default:

• System fonts — fast, native, invisible (good for utility-focused products)
• Geometric sans (Geist, Inter) — modern, clean, technical
• Humanist sans (SF Pro, Satoshi) — warmer, more approachable
• Monospace influence — technical, developer-focused, data-heavy

Part 2: Craft Principles

These apply regardless of design direction. This is the quality floor.

The 4px Grid

All spacing uses a 4px base grid:
- 4px - micro spacing (icon gaps)
- 8px - tight spacing (within components)
- 12px - standard spacing (between related elements)
- 16px - comfortable spacing (section padding)
- 24px - generous spacing (between sections)
- 32px - major separation

Symmetrical Padding

TLBR must match. If top padding is 16px, left/bottom/right must also be 16px. Exception: when content naturally creates visual balance.

/* Good */
padding: 16px;
padding: 12px 16px; /* Only when horizontal needs more room */

/* Bad */
padding: 24px 16px 12px 16px;

Border Radius Consistency

Stick to the 4px grid. Sharper corners feel technical, rounder corners feel friendly. Pick a system and commit:

• Sharp: 4px, 6px, 8px
• Soft: 8px, 12px
• Minimal: 2px, 4px, 6px

Don't mix systems. Consistency creates coherence.

Depth & Elevation Strategy

Match your depth approach to your design direction. Depth is a tool, not a requirement:

Borders-only (flat) — Clean, technical, dense. Works for utility-focused tools where information density matters more than visual lift. Linear, Raycast, and many developer tools use almost no shadows — just subtle borders to define regions.

Subtle single shadows — Soft lift without complexity. A simple 0 1px 3px rgba(0,0,0,0.08) can be enough.

Layered shadows — Rich, premium, dimensional. Multiple shadow layers create realistic depth. Stripe and Mercury use this approach.

Surface color shifts — Background tints establish hierarchy without any shadows. A card at #fff on a #f8fafc background already feels elevated.

Choose ONE approach and commit.

/* Borders-only approach */
--border: rgba(0, 0, 0, 0.08);
border: 0.5px solid var(--border);

/* Single shadow approach */
--shadow: 0 1px 3px rgba(0, 0, 0, 0.08);

/* Layered shadow approach */
--shadow-layered:
  0 0 0 0.5px rgba(0, 0, 0, 0.05),
  0 1px 2px rgba(0, 0, 0, 0.04),
  0 2px 4px rgba(0, 0, 0, 0.03),
  0 4px 8px rgba(0, 0, 0, 0.02);

Card Layouts

Monotonous card layouts are lazy design. Design each card's internal structure for its specific content — but keep the surface treatment consistent: same border weight, shadow depth, corner radius, padding scale, typography.

Isolated Controls

UI controls deserve container treatment. Date pickers, filters, dropdowns should feel like crafted objects.

Never use native form elements for styled UI. Build custom components instead:
- Custom select: trigger button + positioned dropdown menu
- Custom date picker: input + calendar popover
- Custom checkbox/radio: styled div with state management

Typography Hierarchy

• Headlines: 600 weight, tight letter-spacing (-0.02em)
• Body: 400-500 weight, standard tracking
• Labels: 500 weight, slight positive tracking for uppercase
• Scale: 11px, 12px, 13px, 14px (base), 16px, 18px, 24px, 32px

Monospace for Data

Numbers, IDs, codes, timestamps belong in monospace. Use tabular-nums for columnar alignment.

Iconography

Use Phosphor Icons (@phosphor-icons/react) or Lucide (lucide-react). Icons clarify, not decorate — if removing an icon loses no meaning, remove it.

Animation

• 150ms for micro-interactions, 200-250ms for larger transitions
• Easing: cubic-bezier(0.25, 1, 0.5, 1)
• No spring/bouncy effects in enterprise UI

Contrast Hierarchy

Build a four-level system: foreground (primary) → secondary → muted → faint. Use all four consistently.

Color for Meaning Only

Gray builds structure. Color only appears when it communicates: status, action, error, success. Decorative color is noise.

Navigation Context

Screens need grounding:
- Navigation — sidebar or top nav showing where you are
- Location indicator — breadcrumbs, page title, or active nav state
- User context — who's logged in, what workspace/org

Dark Mode Considerations

Borders over shadows — Shadows are less visible on dark backgrounds. Lean more on borders.

Adjust semantic colors — Status colors often need to be slightly desaturated for dark backgrounds.

Part 3: Anti-Patterns

Never Do This

• Dramatic drop shadows (box-shadow: 0 25px 50px...)
• Large border radius (16px+) on small elements
• Asymmetric padding without clear reason
• Pure white cards on colored backgrounds
• Thick borders (2px+) for decoration
• Excessive spacing (margins > 48px between sections)
• Spring/bouncy animations
• Gradients for decoration
• Multiple accent colors in one interface

Always Question

• "Did I think about what this product needs, or did I default?"
• "Does this direction fit the context and users?"
• "Does this element feel crafted?"
• "Is my depth strategy consistent and intentional?"
• "Are all elements on the grid?"

Part 4: Style Guide Template

The style guide is living documentation of your design system. Every component you build should be documented here.

What the Template Creates

A /style-guide page with:
- Left navigation — Sticky sidebar with hierarchical section navigation
- Colors — Brand palette, category colors, system colors
- Typography — Font families, sizes, weights
- Buttons — All variants, sizes, states
- Inputs — Default, focus, error, disabled states
- Cards — Layout variations
- Avatars — Sizes and fallback states
- Dialogs — Modal patterns
- Loading/Thinking — Spinners, indicators, animated states
- Design Tokens — Spacing scale, border radius, shadows

Using the Template

1. Copy to Your Project

cp templates/style-guide-page.tsx your-app/app/style-guide/page.tsx

2. Customize

1. Update the header title — Replace "STYLE GUIDE" with your project name
2. Add your brand colors — Update the Colors section with your palette
3. Add your fonts — Update the Typography section
4. Import your components — Replace placeholder imports with your actual components
5. Add project-specific sections — Add sections for custom components

3. Maintain

The style guide is the canonical source for all UI components.

When building or modifying components:

1. Check the style guide first — See if a component exists before creating
2. Add new components — Every reusable component gets a section
3. Show all states — Normal, hover, focus, disabled, error, loading
4. Update on changes — Modify a component? Update its style guide entry

Template Structure

Navigation items define the sidebar structure:

const NAV_ITEMS = [
  { id: 'colors', label: 'Colors', icon: Palette, children: [
    { id: 'brand', label: 'Brand' },
    { id: 'system', label: 'System' },
  ]},
  { id: 'typography', label: 'Typography', icon: Type },
  { id: 'buttons', label: 'Buttons', icon: MousePointer },
  // ... more sections
]

Each section follows this pattern:

<section id="buttons">
  <SectionHeader title="Buttons" />
  <div>
    <h4 className="text-xs font-medium text-muted-foreground mb-3 uppercase tracking-wide">
      Variants
    </h4>
    <div className="flex flex-wrap gap-3">
      <Button variant="default">Default</Button>
      <Button variant="secondary">Secondary</Button>
    </div>
  </div>
</section>

Adding Custom Sections

1. Add to NAV_ITEMS:

{ id: 'my-component', label: 'My Component', icon: Box },

1. Add the section:

<section id="my-component">
  <SectionHeader title="My Component" />
  {/* Component variations */}
</section>

Maintenance Checklist

For every UI change:

• [ ] Component added to style guide (if new)
• [ ] All states shown (normal, hover, disabled, loading, error)
• [ ] Uses design tokens (colors, spacing, radius from theme)
• [ ] Properly exported from component index

Best Practices

1. Keep it current — Outdated style guides are worse than none
2. Show real data — Use realistic mock data, not "Lorem ipsum"
3. Test interactions — Dialogs should open, buttons should click
4. Document edge cases — Long text, empty states, loading
5. Mobile considerations — Show responsive variants if applicable

The Standard

Every interface should look designed by a team that obsesses over 1-pixel differences. Not stripped — crafted. And designed for its specific context.

The goal: intricate minimalism with appropriate personality. Same quality bar, context-driven execution.