Implement Design System

Read DESIGN.md and apply its tokens to the project's existing style files.

DESIGN.md Discovery

Find DESIGN.md using this search order:

1. Check CLAUDE.md in cwd for a reference to DESIGN.md
2. Look for DESIGN.md in cwd
3. Search upward from cwd
4. Search common locations: project root, src/, packages/*/
5. If not found, tell the user: "No DESIGN.md found. Run /design-systems:create first."

Use Glob to search: **/DESIGN.md

Implementation Flow

Step 1: Parse the Design System

Extract all implementable tokens from DESIGN.md:

• Colors: Every hex value with its token name from the Palette subsection
• Typography: Font families, sizes (rem), weights, line-heights from the Type Scale table
• Spacing: Base unit and all derived values from the Spacing Scale table
• Shadows: Exact CSS values from Shadow Definitions
• Radius: Border-radius values from the Components section
• Any other CSS-expressible values mentioned in the schema

Step 2: Detect Framework/CSS Setup

Scan the project for the styling approach:

Indicator	Framework	Token Format
tailwind.config.* present	Tailwind CSS	Extend theme in config file
*.module.css or *.module.scss files	CSS Modules	CSS custom properties in global stylesheet
styled-components or @emotion in package.json	CSS-in-JS	Theme object exported from a theme file
*.css or *.scss files present	Vanilla CSS/SCSS	CSS custom properties in a variables file
*.vue files with <style> blocks	Vue SFC	CSS custom properties in global stylesheet
*.svelte files with <style> blocks	Svelte	CSS custom properties in global stylesheet
None detected	Unknown	Ask user; default to CSS custom properties

Use Glob to detect: **/tailwind.config.*, **/*.module.css, **/*.module.scss, **/*.vue, **/*.svelte. Use Grep to check package.json for styled-components or @emotion.

Step 3: Apply Tokens

Based on the detected framework:

CSS Custom Properties (default for vanilla CSS, CSS Modules, Vue, Svelte):

Create or update a tokens file with all design tokens:

:root {
  /* Colors — Surface */
  --surface: #value;
  --surface-dim: #value;
  --surface-bright: #value;
  --surface-container-lowest: #value;
  --surface-container-low: #value;
  --surface-container: #value;
  --surface-container-high: #value;
  --surface-container-highest: #value;

  /* Colors — Primary */
  --primary: #value;
  --primary-container: #value;
  --on-primary: #value;
  --on-primary-container: #value;

  /* Colors — Secondary */
  --secondary: #value;
  --secondary-container: #value;
  --on-secondary: #value;
  --on-secondary-container: #value;

  /* Colors — Tertiary */
  --tertiary: #value;
  --tertiary-container: #value;
  --on-tertiary: #value;
  --on-tertiary-container: #value;

  /* Colors — Outline */
  --outline: #value;
  --outline-variant: #value;

  /* Colors — On Surface */
  --on-surface: #value;
  --on-surface-variant: #value;

  /* Typography */
  --font-display: 'Font Name', fallback;
  --font-body: 'Font Name', fallback;
  --font-mono: 'Font Name', monospace;

  /* Spacing */
  --spacing-1: 0.25rem;
  --spacing-2: 0.5rem;
  /* ... all spacing tokens ... */

  /* Shadows */
  --shadow-sm: /* value */;
  --shadow-md: /* value */;
  --shadow-lg: /* value */;

  /* Radius */
  --radius-sm: /* value */;
  --radius-md: /* value */;
  --radius-lg: /* value */;
}

Place the tokens file at:

• If a variables.css, _variables.scss, or similar exists: update it
• Otherwise: create design-tokens.css next to DESIGN.md

Tailwind CSS:

Extend the existing tailwind.config.* file's theme:

// Add to theme.extend
colors: {
  surface: { DEFAULT: '#value', dim: '#value', bright: '#value', ... },
  primary: { DEFAULT: '#value', container: '#value' },
  // ... map all color tokens
},
fontFamily: {
  display: ['Font Name', 'fallback'],
  body: ['Font Name', 'fallback'],
  mono: ['Font Name', 'monospace'],
},
spacing: {
  // ... map spacing scale
},
boxShadow: {
  // ... map shadow tokens
},
borderRadius: {
  // ... map radius tokens
},

CSS-in-JS (styled-components, emotion):

Create or update a theme file:

export const theme = {
  colors: {
    surface: { default: '#value', dim: '#value', ... },
    primary: { default: '#value', container: '#value' },
    // ...
  },
  fonts: {
    display: "'Font Name', fallback",
    body: "'Font Name', fallback",
    mono: "'Font Name', monospace",
  },
  spacing: { ... },
  shadows: { ... },
  radii: { ... },
} as const;

Step 4: Replace Hardcoded Values (Optional)

If existing CSS files contain hardcoded values that match DESIGN.md tokens, offer to replace them with variable references. Show the user what will change:

Found 12 hardcoded values matching design tokens:
- src/styles/global.css:14 — #1a1a1a → var(--surface)
- src/styles/global.css:28 — #0052FF → var(--primary)
...
Replace these with token references? [y/n]

Step 5: Report

Tell the user:

• Files created or modified (with paths)
• Number of tokens defined
• Any DESIGN.md values that couldn't be mapped
• Suggest: "Run /design-systems:review to verify your existing code matches the new tokens"

In-Session Agent Guidance

After completing the implementation, follow these rules for the rest of the session when writing any UI code:

• Surface hierarchy: Use DESIGN.md's layering rules to choose backgrounds
• Typography: Match content type to the type scale (headlines → display/headline, body → body-md, data → label with mono)
• Spacing: Derive all values from the spacing scale. Never invent new values.
• Prohibitions: Respect Core Prohibitions unconditionally
• Edge cases: Use the closest defined token. Do not introduce new values.