vite build produces incorrectly flattened nested CSS

[RobinMalfait]

Describe the bug

When using modern CSS with nesting, a production build will generate invalid CSS.

Given the following CSS:

.foo {
  :where(& > .bar) {
    color: red;
  }
}

In a production build, this is flattened as:

.foo :where(>.bar){color:red}

This CSS is invalid because :where(…) doesn't accept relative selectors.

But I expect it to be flattened as this instead:

:where(.foo>.bar){color:red}

---

Note: in dev mode (vite dev) it works as expected.

Reproduction

https://github.com/RobinMalfait/vite-incorrect-css-flattening

Steps to reproduce

• npm install
• npm run dev — open http://localhost:5173, the text should be red
• npm run build — open http://localhost:4173, the text should be red, but is black

System Info

System:
    OS: macOS 15.2
    CPU: (10) arm64 Apple M1 Max
    Memory: 3.51 GB / 64.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 18.17.1 - ~/.local/state/fnm_multishells/16285_1734176270818/bin/node
    Yarn: 1.22.22 - ~/.local/state/fnm_multishells/1076_1734173982354/bin/yarn
    npm: 9.6.7 - ~/.local/state/fnm_multishells/16285_1734176270818/bin/npm
    pnpm: 9.8.0 - ~/Library/pnpm/pnpm
    bun: 1.1.39 - ~/.bun/bin/bun
  Browsers:
    Brave Browser: 120.1.61.114
    Chrome: 131.0.6778.140
    Chrome Canary: 133.0.6898.0
    Edge: 124.0.2478.80
    Firefox Nightly: 131.0a1
    Safari: 18.2
    Safari Technology Preview: 18.2
  npmPackages:
    vite: ^6.0.3 => 6.0.3

Used Package Manager

npm

Logs

Click to expand!

❯ vite build --debug
  vite:config no config file found. +0ms
  vite:config using resolved config: {
  vite:config   root: '/Users/robin/github.com/RobinMalfait/vite-incorrect-css-flattening',
  vite:config   base: '/',
  vite:config   mode: 'production',
  vite:config   configFile: undefined,
  vite:config   logLevel: undefined,
  vite:config   clearScreen: undefined,
  vite:config   build: {
  vite:config     target: [ 'es2020', 'edge88', 'firefox78', 'chrome87', 'safari14' ],
  vite:config     polyfillModulePreload: true,
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  vite:config     outDir: 'dist',
  vite:config     assetsDir: 'assets',
  vite:config     assetsInlineLimit: 4096,
  vite:config     sourcemap: false,
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  vite:config     rollupOptions: {},
  vite:config     commonjsOptions: { include: [ /node_modules/ ], extensions: [ '.js', '.cjs' ] },
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  vite:config     emptyOutDir: null,
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  vite:config     chunkSizeWarningLimit: 500,
  vite:config     watch: null,
  vite:config     cssCodeSplit: true,
  vite:config     minify: 'esbuild',
  vite:config     ssr: false,
  vite:config     emitAssets: true,
  vite:config     createEnvironment: [Function: createEnvironment],
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  vite:config     cssMinify: true
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  vite:config   assetsInclude: [Function: assetsInclude],
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  vite:config   },
  vite:config   packageCache: Map(1) {
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  vite:config       dir: '/Users/robin/github.com/RobinMalfait/vite-incorrect-css-flattening',
  vite:config       data: {
  vite:config         name: 'vite-incorrect-css-flattening',
  vite:config         version: '1.0.0',
  vite:config         description: '',
  vite:config         main: 'index.js',
  vite:config         scripts: { dev: 'vite dev', build: 'vite build && vite preview' },
  vite:config         keywords: [],
  vite:config         author: 'Robin Malfait',
  vite:config         license: 'ISC',
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  vite:config       },
  vite:config       hasSideEffects: [Function: hasSideEffects],
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  vite:config   future: undefined,
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  vite:config   },
  vite:config   optimizeDeps: {
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  vite:config   fsDenyGlob: [Function: arrayMatcher],
  vite:config   safeModulePaths: Set(0) {}
  vite:config } +13ms
vite v6.0.3 building for production...
✓ 2 modules transformed.
dist/index.html                 0.20 kB │ gzip: 0.15 kB
dist/assets/index-DiaIqj75.css  0.03 kB │ gzip: 0.05 kB
✓ built in 41ms

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Make sure this is a Vite issue and not a framework-specific issue. For example, if it's a Vue SFC related bug, it should likely be reported to vuejs/core instead.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.

[clementgateaud]

Hello! Any news on this issue ? I have the same issue using some tailwind classes on Nuxt.

[engyii]

I +1, Got the same issue here, this CSS from tailwind 4 (beta > 6) is not applied in our nuxt build (3.15.1)

.space-x-2 {
    :where(& > :not(:last-child)) {
      --tw-space-x-reverse: 0;
      margin-inline-start: calc(calc(var(--spacing) * 2) * var(--tw-space-x-reverse));
      margin-inline-end: calc(calc(var(--spacing) * 2) * calc(1 - var(--tw-space-x-reverse)));
    }
  }

became

.space-x-2 :where(>:not(:last-child)) {
                    --tw-space-x-reverse: 0;
                    margin-inline-end:calc(var(--spacing)*2*(1 - var(--tw-space-x-reverse)));margin-inline-start: calc(var(--spacing)*2*var(--tw-space-x-reverse))
                }

The beta version of tailwind 4 is not buildable with vite as a result (or I don't know how)

[evdama]

I've moved my Sveltekit project to Tailwind v4 with Vite yesterday and there I have a utilities.css which among other things has

@utility scrollbar-hidden {
  /* Hide scrollbar for Chrome, Safari and Opera */
  &::-webkit-scrollbar {
    display: none;
  }
  /* Hide scrollbar for IE, Edge and Firefox */
  -ms-overflow-style: none; /* IE and Edge */
  scrollbar-width: none; /* Firefox */
}

This shows up and works in my local dev build using vite dev but is absent from the production build using vite build. My vite.config.ts is rather simple:

import { defineConfig } from 'vitest/config'
import { sveltekit } from '@sveltejs/kit/vite'
import tailwindcss from '@tailwindcss/vite'

export default defineConfig({
  build: { target: 'ESNext' },
  plugins: [sveltekit(), tailwindcss()],
  test: {
    include: ['tests/vitest/**/*.{test,spec}.{js,ts}']
  }
})

I'm currently on those package versions:

sa@Mac: ~/0/ulm  |development ✓| gr vite package.json
package.json:8:    "dev": "vite dev",
package.json:9:    "build": "vite build",
package.json:10:    "preview": "vite preview",
package.json:18:    "tests:unit": "vitest --run",
package.json:28:    "@sveltejs/vite-plugin-svelte": "^5.0.3",
package.json:30:    "@tailwindcss/vite": "4.0.0-beta.9",
package.json:74:    "vite": "^6.0.7",
package.json:75:    "vitest": "^2.1.8",
sa@Mac: ~/0/ulm  |development ✓| gr tailwind package.json
package.json:29:    "@tailwindcss/forms": "^0.5.10",
package.json:30:    "@tailwindcss/vite": "4.0.0-beta.9",
package.json:53:    "prettier-plugin-tailwindcss": "^0.6.9",
package.json:67:    "tailwindcss": "4.0.0-beta.9",
sa@Mac: ~/0/ulm  |development ✓|

[sk31park]

Has anyone resolved this issue?
I'm having the exact same issue with nuxt build.

[Botato300]

same here!
original code:

 .space-x-4 {
    :where(& > :not(:last-child)) {
      --tw-space-x-reverse: 0;
      margin-inline-start: calc(calc(var(--spacing) * 4) * var(--tw-space-x-reverse));
      margin-inline-end: calc(calc(var(--spacing) * 4) * calc(1 - var(--tw-space-x-reverse)));
    }

final code:

.space-x-4 :where(>:not(:last-child)) {
    --tw-space-x-reverse: 0;
    margin-inline-start: calc(calc(var(--spacing) * 4) * var(--tw-space-x-reverse));
    margin-inline-end: calc(calc(var(--spacing) * 4) * calc(1 - var(--tw-space-x-reverse)))
    }

[dargmuesli]

Upstream issue was fixed, will likely be part of the next esbuild release.

[dargmuesli]

v0.25.0 of esbuild has been released 🥳

[evdama]

@RobinMalfait do you know when this will fix the issue in tailwind? I'm currently on 4.0.5 and the issue is still present i.e. works in dev mode but the production build is broken.

[RobinMalfait]

@evdama it's not a Tailwind issue. Tailwind produces valid CSS, and then Vite processes the CSS (or in this case esbuild) and esbuild produced invalid CSS.

This is now fixed in esbuild and released as part of https://github.com/evanw/esbuild/releases/tag/v0.25.0, once Vite bumps the esbuild version then this should start working again.

[evdama]

Thanks! Understood. So now we wait https://github.com/vitejs/vite/blob/main/packages/vite/package.json#L88

[chz]

Temporarily fix:

install lightningcss (bun|pnpm|npm) im my case bun.

nuxt.config.ts:

  vite: {
    // ...
    build: {
      cssMinify: 'lightningcss',
    },
    // ...
  },