Consuming @policyengine/ui-kit

How to correctly import and use the PolicyEngine UI kit's design system in any consumer application. This skill covers the required setup, the correct import order, and common mistakes that cause styling to break.

Required Consumer Setup

Every app using @policyengine/ui-kit needs exactly three things:

1. Install dependencies

bun add @policyengine/ui-kit
bun add -D @tailwindcss/postcss postcss

2. Create postcss.config.mjs

export default {
  plugins: {
    "@tailwindcss/postcss": {},
  },
};

No other PostCSS plugins needed — @tailwindcss/postcss handles imports, vendor prefixes, and nesting internally.

3. Create app/globals.css with two imports

@import "tailwindcss";
@import "@policyengine/ui-kit/theme.css";

Both lines are required. The order matters. Tailwind must come first because the ui-kit's @theme blocks extend it.

This provides:

• All Tailwind v4 utility classes (flex, grid, p-4, text-sm, etc.)
• All PolicyEngine design tokens (colors, fonts, spacing, breakpoints)
• shadcn/ui semantic tokens (bg-primary, text-foreground, border-border)
• Brand palette (bg-teal-500, text-gray-600, bg-blue-500)
• Base element styles (body font, border defaults, slider styling)

How It Works

Understanding the flow prevents debugging confusion:

1. The consumer's build tool (Next.js/Vite) processes globals.css through @tailwindcss/postcss
2. @import "tailwindcss" establishes the cascade layers and enables utility class generation
3. Tailwind's automatic source detection scans from process.cwd() (the consumer's project root) — this is why the consumer's utility classes get generated
4. @import "@policyengine/ui-kit/theme.css" is inlined by Tailwind's import bundler
5. The ui-kit's @theme and @theme inline blocks merge into the consumer's Tailwind build
6. The ui-kit's @source directive tells Tailwind to also scan the ui-kit's own component files
7. The ui-kit's @layer base styles apply within the existing cascade

What NOT to Do

Do NOT skip the Tailwind import

/* WRONG — utility classes will not be generated */
@import "@policyengine/ui-kit/theme.css";

/* CORRECT */
@import "tailwindcss";
@import "@policyengine/ui-kit/theme.css";

Without @import "tailwindcss", there is no Tailwind build. The ui-kit's @theme blocks have nothing to extend. No utility classes (flex, p-4, grid) will exist.

Do NOT add a duplicate Tailwind import

/* WRONG — double Tailwind causes conflicting resets and broken styles */
@import "tailwindcss";
@import "@policyengine/ui-kit/theme.css";
@import "tailwindcss";

The ui-kit does NOT contain @import "tailwindcss" inside it. One import at the top of globals.css is all that's needed.

Do NOT create tailwind.config.ts

/* WRONG — Tailwind v4 does not use JavaScript config */
tailwind.config.ts  ← DELETE THIS

Tailwind v4 is CSS-first. All configuration comes from @theme blocks in the ui-kit's theme CSS. There is no content array, no theme.extend, no JavaScript config.

Do NOT add postcss-import or autoprefixer

/* WRONG — these conflict with @tailwindcss/postcss */
export default {
  plugins: {
    "postcss-import": {},
    "@tailwindcss/postcss": {},
    "autoprefixer": {},
  },
};

/* CORRECT — @tailwindcss/postcss handles both internally */
export default {
  plugins: {
    "@tailwindcss/postcss": {},
  },
};

Do NOT put @import "tailwindcss" inside the ui-kit package

If working on the ui-kit itself, never add @import "tailwindcss" to tokens.css. The consumer owns that import. See tailwind-design-system-authoring skill for details.

Do NOT hardcode hex colors or font names

/* WRONG */
<div style={{ color: '#319795', fontFamily: 'Inter' }}>

/* CORRECT — use Tailwind classes */
<div className="text-teal-500 font-sans">

/* CORRECT — use CSS variables for inline styles */
<div style={{ color: 'var(--primary)', fontFamily: 'var(--font-sans)' }}>

Troubleshooting

"No styles at all" — page is unstyled

1. Verify globals.css has @import "tailwindcss" as the first line
2. Verify postcss.config.mjs exists with @tailwindcss/postcss
3. Verify @tailwindcss/postcss and postcss are installed as devDependencies
4. Verify globals.css is imported in app/layout.tsx (or pages/_app.tsx)

"Tokens load but no utility classes" — colors work but no flex/grid/padding

This means @theme tokens are being processed but Tailwind's utility generation isn't scanning files correctly.

If missing classes are from the consumer's own components (app/, components/):

1. Verify @import "tailwindcss" comes BEFORE the ui-kit import (order matters)
2. Check that process.cwd() is the project root when the build runs
3. If in a monorepo, add source() to the import: @import "tailwindcss" source("./src")

If missing classes are from ui-kit components (DashboardShell, Header, InputPanel, etc.): The ui-kit's @source directive in tokens.css may not match the actual directory structure. This is a ui-kit-side fix — the @source glob must cover all directories containing .tsx files with className= attributes. See the tailwind-design-system-authoring skill for the verification procedure.

"Double styling / Tailwind defaults override tokens"

This means Tailwind is being imported twice.

1. Check that the ui-kit's tokens.css does NOT contain @import "tailwindcss"
2. Check that globals.css has only ONE @import "tailwindcss" line
3. Check for other CSS files that might import Tailwind

"Utility classes from ui-kit components missing"

The ui-kit ships @source directives to tell Tailwind to scan its components. If this fails:

1. Add a manual @source in globals.css:
   cssCopy

   @import "tailwindcss";
   @import "@policyengine/ui-kit/theme.css";
   @source "../node_modules/@policyengine/ui-kit/src";
   

2. If using bun link (symlinked package), the path resolves differently — check the actual resolved path

Framework-Specific Notes

Next.js 14 (App Router)

Standard setup. Requires @tailwindcss/postcss in PostCSS config.

app/
  globals.css    ← @import "tailwindcss"; @import ui-kit theme
  layout.tsx     ← import "./globals.css";
postcss.config.mjs

Next.js 15+ / Next.js 16

Same setup. Turbopack processes PostCSS normally. No changes needed.

Vite (non-Next.js)

Use @tailwindcss/vite instead of @tailwindcss/postcss:

// vite.config.ts
import tailwindcss from '@tailwindcss/vite'
export default defineConfig({ plugins: [tailwindcss()] })

No postcss.config.mjs needed — the Vite plugin handles everything.

globals.css is the same two imports.

Quick Reference

What the Theme Provides

After the two-line import, these are available:

Related Skills

• policyengine-design-skill — Full token reference (hex values, usage guidelines)
• policyengine-tailwind-shadcn-skill — @theme namespace mechanics, SVG var() usage
• policyengine-interactive-tools-skill — Full tool scaffolding checklist
• policyengine-vercel-deployment-skill — Deploying consumer apps