Name: tailwind-theme-builder
Availability: InStock
Author: jezweb
Set up Tailwind v4 + shadcn/ui themed UI with dark mode. Install deps, configure CSS variables via @theme inline, wire dark mode toggle, verify. Use whenever…
SKILL.md

Tailwind Theme Builder

Set up a fully themed Tailwind v4 + shadcn/ui project with dark mode. Produces configured CSS, theme provider, and working component library.

Architecture: The Four-Step Pattern

Tailwind v4 requires a specific architecture for CSS variable-based theming. This pattern is mandatory -- skipping or modifying steps breaks the theme.

How It Works

CSS Variable Definition --> @theme inline Mapping --> Tailwind Utility Class
--background           --> --color-background     --> bg-background
(with hsl() wrapper)      (references variable)     (generated class)

Dark mode switching:

ThemeProvider toggles .dark class on <html>
  --> CSS variables update automatically (.dark overrides :root)
  --> Tailwind utilities reference updated variables
  --> UI updates without re-render

Best Practices

Semantic names: Use --primary not --blue-500

Foreground pairing: Every background colour needs a foreground (--primary + --primary-foreground)

WCAG contrast: Normal text 4.5:1, large text 3:1, UI components 3:1

Chart colours: Use separate variables with @theme inline mapping, reference via var(--chart-1) in style props

Workflow

Step 1: Install Dependencies

pnpm add tailwindcss @tailwindcss/vite
pnpm add -D @types/node tw-animate-css
pnpm dlx shadcn@latest init

# Delete v3 config if it exists
rm -f tailwind.config.ts

Step 2: Configure Vite

Copy assets/vite.config.ts or add the Tailwind plugin:

import { defineConfig } from 'vite'
import react from '@vitejs/plugin-react'
import tailwindcss from '@tailwindcss/vite'
import path from 'path'

export default defineConfig({
  plugins: [react(), tailwindcss()],
  resolve: { alias: { '@': path.resolve(__dirname, './src') } }
})

Step 3: Four-Step CSS Architecture (Mandatory)

This exact order is required. Skipping steps breaks the theme.

src/index.css:

@import "tailwindcss";
@import "tw-animate-css";

/* 1. Define CSS variables at root (NOT inside @layer base) */
:root {
  --background: hsl(0 0% 100%);
  --foreground: hsl(222.2 84% 4.9%);
  --primary: hsl(221.2 83.2% 53.3%);
  --primary-foreground: hsl(210 40% 98%);
  /* ... all semantic tokens */
}

.dark {
  --background: hsl(222.2 84% 4.9%);
  --foreground: hsl(210 40% 98%);
  --primary: hsl(217.2 91.2% 59.8%);
  --primary-foreground: hsl(222.2 47.4% 11.2%);
}

/* 2. Map variables to Tailwind utilities */
@theme inline {
  --color-background: var(--background);
  --color-foreground: var(--foreground);
  --color-primary: var(--primary);
  --color-primary-foreground: var(--primary-foreground);
}

/* 3. Apply base styles (NO hsl() wrapper here) */
@layer base {
  body {
    background-color: var(--background);
    color: var(--foreground);
  }
}

Result: bg-background, text-primary etc. work automatically. Dark mode switches via .dark class -- no dark: variants needed for semantic colours.

Step 4: Set Up Dark Mode

Copy assets/theme-provider.tsx to your components directory, then wrap your app:

import { ThemeProvider } from '@/components/theme-provider'

ReactDOM.createRoot(document.getElementById('root')!).render(
  <ThemeProvider defaultTheme="dark" storageKey="vite-ui-theme">
    <App />
  </ThemeProvider>
)

Add a theme toggle -- install the dropdown menu then use the ModeToggle component below:

pnpm dlx shadcn@latest add dropdown-menu

// src/components/mode-toggle.tsx
import { Moon, Sun } from "lucide-react"
import { Button } from "@/components/ui/button"
import {
  DropdownMenu,
  DropdownMenuContent,
  DropdownMenuItem,
  DropdownMenuTrigger,
} from "@/components/ui/dropdown-menu"
import { useTheme } from "@/components/theme-provider"

export function ModeToggle() {
  const { setTheme } = useTheme()

  return (
    <DropdownMenu>
      <DropdownMenuTrigger asChild>
        <Button variant="outline" size="icon">
          <Sun className="h-[1.2rem] w-[1.2rem] rotate-0 scale-100 transition-all dark:-rotate-90 dark:scale-0" />
          <Moon className="absolute h-[1.2rem] w-[1.2rem] rotate-90 scale-0 transition-all dark:rotate-0 dark:scale-100" />
          <span className="sr-only">Toggle theme</span>
        </Button>
      </DropdownMenuTrigger>
      <DropdownMenuContent align="end">
        <DropdownMenuItem onClick={() => setTheme("light")}>Light</DropdownMenuItem>
        <DropdownMenuItem onClick={() => setTheme("dark")}>Dark</DropdownMenuItem>
        <DropdownMenuItem onClick={() => setTheme("system")}>System</DropdownMenuItem>
      </DropdownMenuContent>
    </DropdownMenu>
  )
}

Step 5: Configure components.json

{
  "tailwind": {
    "config": "",
    "css": "src/index.css",
    "baseColor": "slate",
    "cssVariables": true
  }
}

"config": "" is critical -- v4 doesn't use tailwind.config.ts.

Critical Rules

Always:

Wrap colours with hsl() in :root/.dark

Use @theme inline to map all CSS variables

Use @tailwindcss/vite plugin (NOT PostCSS)

Delete tailwind.config.ts if it exists

Never:

Put :root/.dark inside @layer base

Use .dark { @theme { } } (v4 doesn't support nested @theme)

Double-wrap: hsl(var(--background))

Use @apply with @layer base classes (use @utility instead)

All 18 Gotchas

Quick Diagnosis

#
Symptom
Cause
Fix

1
Variables ignored / theme broken
:root inside @layer base
Move :root and .dark to root level

2
Dark mode colours not switching
.dark { @theme { } }
Use CSS variables + single @theme inline

3
Colours all black/white
Double hsl() wrapping
Use var(--background) not hsl(var(...))

4
bg-primary not generated
Colours in tailwind.config.ts
Delete config, use @theme inline

5
bg-background class missing
No @theme inline block
Add @theme inline mapping variables

6
shadcn components break
components.json has config path
Set "config": "" (empty string)

7
Tailwind not processing
Using PostCSS plugin
Switch to @tailwindcss/vite plugin

8
@/ imports fail
Missing path aliases
Add paths to tsconfig.app.json

9
Redundant dark: variants
Using dark:bg-primary-dark
Just use bg-primary -- variables handle it

10
Hardcoded colours everywhere
Using bg-blue-600 dark:bg-blue-400
Use semantic tokens: bg-primary

11
Class merging bugs
String concatenation for classes
Use cn() from @/lib/utils

12
Radix Select crashes
Empty string value value=""
Use value="placeholder"

13
Wrong Tailwind version
Installed tailwindcss@^3
Install tailwindcss@^4.1.0 + @tailwindcss/vite

14
Missing peer deps
Only installed tailwindcss
Also install clsx, tailwind-merge, @types/node

15
Broken in dark mode
Only tested light mode
Test light, dark, system, and toggle transitions

16
Fails WCAG contrast
Looks fine visually
Check ratios: 4.5:1 normal text, 3:1 large/UI

17
Build fails on animation import
Using tailwindcss-animate (deprecated)
Use tw-animate-css or native CSS animations

18
CSS priority issues
Duplicate @layer base after shadcn init
Merge into single @layer base block

Gotcha Details with Code Examples

#1 -- :root inside @layer base

Tailwind v4 strips CSS outside @theme/@layer, but :root must be at root level to persist. This is the most common setup failure.

WRONG:

@layer base {
  :root { --background: hsl(0 0% 100%); }
}

CORRECT:

:root { --background: hsl(0 0% 100%); }
@layer base {
  body { background-color: var(--background); }
}

#2 -- Nested @theme

Tailwind v4 does not support @theme inside selectors. Use CSS variables in :root/.dark with a single @theme inline block.

WRONG:

@theme { --color-primary: hsl(0 0% 0%); }
.dark { @theme { --color-primary: hsl(0 0% 100%); } }

CORRECT:

:root { --primary: hsl(0 0% 0%); }
.dark { --primary: hsl(0 0% 100%); }
@theme inline { --color-primary: var(--primary); }

#3 -- Double hsl() wrapping

Variables already contain hsl(). Double-wrapping creates hsl(hsl(...)).

WRONG: background-color: hsl(var(--background));
CORRECT: background-color: var(--background);

#4 -- Colours in tailwind.config.ts

Tailwind v4 completely ignores theme.extend.colors in config files. Delete the file or leave it empty. Set "config": "" in components.json.

#5 -- Missing @theme inline

Without @theme inline, Tailwind has no knowledge of your CSS variables. Utility classes like bg-background simply won't be generated.

WRONG:

:root { --background: hsl(0 0% 100%); }
/* No @theme inline block -- bg-background won't exist */

CORRECT:

:root { --background: hsl(0 0% 100%); }
@theme inline { --color-background: var(--background); }

#7 -- PostCSS vs Vite plugin

WRONG:

export default defineConfig({
  css: { postcss: './postcss.config.js' }  // Old v3 way
})

CORRECT:

import tailwindcss from '@tailwindcss/vite'
export default defineConfig({
  plugins: [react(), tailwindcss()]  // v4 way
})

#8 -- Path aliases

Add to tsconfig.app.json:

{
  "compilerOptions": {
    "baseUrl": ".",
    "paths": { "@/*": ["./src/*"] }
  }
}

#11 -- cn() utility for class merging

WRONG: className={`base ${isActive && 'active'}`}
CORRECT: className={cn("base", isActive && "active")}

cn() from @/lib/utils properly merges and deduplicates Tailwind classes.

#12 -- Radix Select empty value

Radix UI Select does not allow empty string values. Use value="placeholder" instead of value="".

#14 -- Required dependencies

{
  "dependencies": {
    "tailwindcss": "^4.1.0",
    "@tailwindcss/vite": "^4.1.0",
    "clsx": "^2.1.1",
    "tailwind-merge": "^3.3.1"
  },
  "devDependencies": {
    "@types/node": "^24.0.0"
  }
}

#17 -- tw-animate-css

tailwindcss-animate is deprecated in Tailwind v4. shadcn/ui docs may still reference it. Causes build failures and import errors. Use tw-animate-css or @tailwindcss/motion instead.

#18 -- Duplicate @layer base after shadcn init

shadcn init adds its own @layer base block. Check src/index.css immediately after running init and merge any duplicate blocks into one.

WRONG:

@layer base { body { background-color: var(--background); } }
@layer base { * { border-color: hsl(var(--border)); } }  /* duplicate from shadcn */

CORRECT:

@layer base {
  * { border-color: var(--border); }
  body { background-color: var(--background); color: var(--foreground); }
}

Prevention Checklist

 No tailwind.config.ts file (or it's empty)

 components.json has "config": ""

 All colors have hsl() wrapper in :root

 @theme inline maps all variables

 @layer base doesn't wrap :root

 Theme provider wraps app

 Tested in light, dark, and system modes

 All text has sufficient contrast

Dark Mode Testing Checklist

 Light mode displays correctly

 Dark mode displays correctly

 System mode respects OS setting

 Theme persists after page refresh

 Toggle component shows current state

 All text has proper contrast

 No flash of wrong theme on load

 Works in incognito mode (graceful fallback)

Asset Files

Copy from assets/ directory:

index.css -- Complete CSS with all colour variables

components.json -- shadcn/ui v4 config

vite.config.ts -- Vite + Tailwind plugin

theme-provider.tsx -- Dark mode provider

utils.ts -- cn() utility

Reference Files

references/migration-guide.md -- v3 to v4 migration

Official Documentation

shadcn/ui Tailwind v4 Guide: https://ui.shadcn.com/docs/tailwind-v4

shadcn/ui Dark Mode (Vite): https://ui.shadcn.com/docs/dark-mode/vite

shadcn/ui Theming: https://ui.shadcn.com/docs/theming

Tailwind v4 Docs: https://tailwindcss.com/docs

Tailwind Dark Mode: https://tailwindcss.com/docs/dark-mode
tailwind-theme-builder

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