tailwind-theme-builder

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: