# CSS Design Tokens

> Define and manage design tokens for colors, spacing, typography, and effects in Tailwind CSS

## When to Use

- Establishing a consistent design system across an application
- Mapping brand colors, spacing scales, and typography to Tailwind utilities
- Supporting multiple themes (light/dark, brand variants) via CSS variables
- Bridging design tool tokens (Figma) to code

## Instructions

1. Define tokens as CSS custom properties in your global stylesheet. Reference them in Tailwind config.
2. Use semantic token names (`--color-primary`, `--color-surface`) instead of absolute names (`--blue-500`).
3. Extend Tailwind's theme in `tailwind.config.ts` to map tokens to utility classes.
4. Use CSS variables for values that change at runtime (theme switching). Use static config for values that never change.
5. Structure tokens in layers: primitive (raw values), semantic (purpose-based aliases), component (component-specific).

```css
/* styles/tokens.css — primitive + semantic layers */
@layer base {
  :root {
    /* Primitive tokens — raw values */
    --blue-50: 239 246 255;
    --blue-500: 59 130 246;
    --blue-900: 30 58 138;
    --gray-50: 249 250 251;
    --gray-900: 17 24 39;
    --radius-sm: 0.25rem;
    --radius-md: 0.375rem;
    --radius-lg: 0.5rem;

    /* Semantic tokens — map to purpose */
    --color-primary: var(--blue-500);
    --color-primary-foreground: 255 255 255;
    --color-background: var(--gray-50);
    --color-foreground: var(--gray-900);
    --color-muted: 107 114 128;
    --color-border: 229 231 235;
    --color-destructive: 239 68 68;
    --radius-default: var(--radius-md);
  }

  .dark {
    --color-primary: var(--blue-500);
    --color-primary-foreground: 255 255 255;
    --color-background: 15 23 42;
    --color-foreground: 248 250 252;
    --color-muted: 148 163 184;
    --color-border: 51 65 85;
  }
}
```

```typescript
// tailwind.config.ts
import type { Config } from 'tailwindcss';

const config: Config = {
  content: ['./src/**/*.{ts,tsx}'],
  theme: {
    extend: {
      colors: {
        primary: {
          DEFAULT: 'rgb(var(--color-primary) / <alpha-value>)',
          foreground: 'rgb(var(--color-primary-foreground) / <alpha-value>)',
        },
        background: 'rgb(var(--color-background) / <alpha-value>)',
        foreground: 'rgb(var(--color-foreground) / <alpha-value>)',
        muted: 'rgb(var(--color-muted) / <alpha-value>)',
        border: 'rgb(var(--color-border) / <alpha-value>)',
        destructive: 'rgb(var(--color-destructive) / <alpha-value>)',
      },
      borderRadius: {
        DEFAULT: 'var(--radius-default)',
        sm: 'var(--radius-sm)',
        md: 'var(--radius-md)',
        lg: 'var(--radius-lg)',
      },
    },
  },
};

export default config;
```

```tsx
// Usage — semantic utilities
<div className="bg-background text-foreground border-border rounded p-4">
  <h1 className="text-primary">Welcome</h1>
  <button className="bg-primary text-primary-foreground rounded px-4 py-2">Get Started</button>
</div>
// These utilities automatically adapt to light/dark theme via CSS variables
```

## Details

**RGB channel pattern:** Store colors as space-separated RGB channels (`59 130 246`) instead of full values (`#3b82f6`). This enables Tailwind's opacity modifier: `bg-primary/50` generates `rgba(59, 130, 246, 0.5)`.

**Tailwind v4 tokens:** In v4, tokens are defined directly in CSS with `@theme`:

```css
@import 'tailwindcss';

@theme {
  --color-primary: oklch(0.6 0.2 260);
  --color-surface: oklch(0.98 0 0);
  --spacing-18: 4.5rem;
  --font-display: 'Cal Sans', sans-serif;
}
```

**Token hierarchy:**

1. **Primitive:** `--blue-500: 59 130 246` — raw color, never used directly in components
2. **Semantic:** `--color-primary: var(--blue-500)` — purpose-based, used in utilities
3. **Component:** `--button-bg: var(--color-primary)` — optional, for complex component theming

**Figma-to-code workflow:** Export tokens from Figma (via Tokens Studio or Style Dictionary), generate CSS variables, import into your token stylesheet. Changes propagate automatically through the semantic layer.

**Typography tokens:**

```typescript
extend: {
  fontFamily: {
    sans: ['var(--font-sans)', 'system-ui', 'sans-serif'],
    mono: ['var(--font-mono)', 'monospace'],
  },
  fontSize: {
    'display': ['3.5rem', { lineHeight: '1.1', fontWeight: '700' }],
    'heading': ['2rem', { lineHeight: '1.25', fontWeight: '600' }],
  },
},
```

## Source

https://tailwindcss.com/docs/theme

## Process

1. Read the instructions and examples in this document.
2. Apply the patterns to your implementation, adapting to your specific context.
3. Verify your implementation against the details and edge cases listed above.

## Harness Integration

- **Type:** knowledge — this skill is a reference document, not a procedural workflow.
- **No tools or state** — consumed as context by other skills and agents.

## Success Criteria

- The patterns described in this document are applied correctly in the implementation.
- Edge cases and anti-patterns listed in this document are avoided.