# Troubleshooting StyleX Compilation Issues with @astryxdesign/build

> Fix StyleX compilation issues with @astryxdesign/build. Learn how this toolchain uses Vite, Babel, and PostCSS to coordinate library and product styles for seamless development.

- Repository: [Meta/astryx](https://github.com/facebook/astryx)
- Tags: how-to-guide
- Published: 2026-08-05

---

**The `@astryxdesign/build` toolchain fixes StyleX compilation issues by coordinating a Vite plugin, a Babel wrapper, and a PostCSS processor to separate library and product styles while enforcing CSS layer ordering.**

StyleX compilation errors in the Astryx ecosystem typically stem from misconfiguration in this three-part build chain. This guide walks through how these plugins interact, what symptoms indicate specific failures, and how to fix them using source-level configuration options from the [facebook/astryx](https://github.com/facebook/astryx) repository.

## Understanding the @astryxdesign/build Architecture

The build system consists of three coordinated pieces that must all be present for correct StyleX compilation:

| Component | Purpose | Source Location |
|-----------|---------|---------------|
| **Vite plugin** (`astryxStylex()`) | Orchestrates StyleX compilation, injects CSS layer order, splits library vs. product styles | [[`packages/build/src/vite.ts`](https://github.com/facebook/astryx/blob/main/packages/build/src/vite.ts)](https://github.com/facebook/astryx/blob/main/packages/build/src/vite.ts) |
| **Babel plugin** (exposed via `babel` export) | Applies different `classNamePrefix` values to prevent collisions | [[`packages/build/src/babel.js`](https://github.com/facebook/astryx/blob/main/packages/build/src/babel.js)](https://github.com/facebook/astryx/blob/main/packages/build/src/babel.js) |
| **PostCSS plugin** (exposed via `postcss` function) | Processes emitted CSS into proper layer order, runs LightningCSS optimization | [[`packages/build/src/config.js`](https://github.com/facebook/astryx/blob/main/packages/build/src/config.js)](https://github.com/facebook/astryx/blob/main/packages/build/src/config.js) |

Each piece handles a distinct phase of the build. The Vite plugin manages the compilation entry point and dev server behavior. The Babel wrapper distinguishes between Astryx library code and consuming application code. The PostCSS plugin finalizes CSS output with layer enforcement.

## Common StyleX Compilation Failures and Fixes

### "StyleX classNamePrefix is wrong / collisions appear"

This occurs when the Babel wrapper isn't applied to the compilation pipeline.

**Root cause:** The [`babel.js`](https://github.com/facebook/astryx/blob/main/babel.js) wrapper decides at compile time whether a file belongs to the Astryx library (matched by `libraryPattern`, defaulting to `node_modules/@astryxdesign/`) or product code, then applies the corresponding prefix: `astryx` for library, `x` for product. Without this wrapper, both namespaces use the same prefix, causing runtime collisions.

**Fix:** Add the Babel export to your configuration:

```js
// babel.config.js
module.exports = {
  presets: ['@babel/preset-react'],
  plugins: [
    // other plugins
    ...require('@astryxdesign/build').babel,
  ],
};

```

### "No CSS is emitted / empty stylesheet"

Vite's dependency optimization can pre-bundle Astryx source files, stripping `stylex.create` calls before StyleX processes them.

**Root cause:** The `optimizeDeps` pre-bundling step treats `@astryxdesign/*` packages as external dependencies and runs them through esbuild, which doesn't preserve StyleX's compile-time CSS extraction.

**Fix:** The `astryxStylex()` plugin automatically populates `optimizeDeps.exclude` with all `@astryxdesign/*` packages. Verify your Vite config doesn't override this:

```ts
// vite.config.ts
import {defineConfig} from 'vite';
import {astryxStylex} from '@astryxdesign/build/vite';

export default defineConfig({
  // Don't manually set optimizeDeps here without merging
  plugins: [...astryxStylex()],
});

```

### "Layer ordering is wrong — library styles override component styles"

CSS cascade layers enforce specificity order. Astryx uses `@layer reset, astryx-base, astryx-theme, product` with library styles in `astryx-base` and product styles in `product`.

**Root cause:** The layer order declaration is missing from the HTML head, or the split-layer interceptor isn't running during dev server CSS generation.

**Fix:** Ensure the `astryx-css-layer-order` plugin runs. In [[`vite.ts`](https://github.com/facebook/astryx/blob/main/vite.ts)](https://github.com/facebook/astryx/blob/main/packages/build/src/vite.ts), this plugin injects the `@layer` declaration into the HTML head. The split-layer interceptor in the dev middleware separates rules by `libraryPattern` and wraps them in their respective `@layer` blocks.

### "light-dark() is compiled to unsupported CSS"

Older StyleX versions polyfill `light-dark()` based on browser targets. Mismatched targets cause unsupported CSS output.

**Root cause:** The LightningCSS pass doesn't receive correct browser targets, or StyleX's own polyfill conflicts with native support.

**Fix:** Provide explicit targets in the Vite plugin options:

```ts
// vite.config.ts
import {defineConfig} from 'vite';
import {astryxStylex} from '@astryxdesign/build/vite';

export default defineConfig({
  plugins: [
    ...astryxStylex({
      lightningcssTargets: {
        chrome: 120 << 16,  // Chrome 120
        firefox: 121 << 16,
        safari: 17 << 16,
      },
    }),
  ],
});

```

### "StyleX compilation errors about unknown tokens"

Design tokens must resolve to their compiled source location, not a non-existent path.

**Root cause:** The Vite plugin's `resolve.alias` entry maps `@astryxdesign/core/theme/tokens.stylex` to the actual source file. If this alias fails or is overridden, StyleX cannot locate token definitions.

**Fix:** Verify no custom Vite `resolve.alias` conflicts with the plugin's internal alias configuration.

## How the Plugins Coordinate

The compilation flow in `@astryxdesign/build` follows this sequence:

1. **Vite initialization** (`astryxStylex()` in [[`vite.ts`](https://github.com/facebook/astryx/blob/main/vite.ts)](https://github.com/facebook/astryx/blob/main/packages/build/src/vite.ts)) builds a StyleX options object with `dev` mode, `unstable_moduleResolution`, optional LightningCSS targets, and user overrides from `stylexOverrides`.

2. **Babel wrapper injection** adds [`babel.js`](https://github.com/facebook/astryx/blob/main/babel.js) to the unplugin's Babel configuration. The wrapper's `processStylexRules` function tags each style rule as library or product based on `libraryPattern` matching.

3. **Dev server CSS generation** serves `virtual:stylex.css` through the split-layer interceptor. This reads the shared StyleX store, separates rules by origin, adds `@layer` information via `processStylexRules`, and returns CSS blocks wrapped in `@layer astryx-base { … }` and `@layer product { … }`.

4. **PostCSS finalization** runs after Vite build (or standalone) to rewrite layer rules, apply LightningCSS optimizations, and ensure final CSS respects the hierarchy defined in [[`packages/build/src/config.js`](https://github.com/facebook/astryx/blob/main/packages/build/src/config.js)](https://github.com/facebook/astryx/blob/main/packages/build/src/config.js).

**Critical requirement:** All three pieces must be present. Dropping any one breaks the library/product style separation, typically manifesting as missing CSS or class name collisions.

## Configuration Examples

### Minimal Vite Setup

```ts
// vite.config.ts
import {defineConfig} from 'vite';
import {astryxStylex} from '@astryxdesign/build/vite';
import react from '@vitejs/plugin-react';

export default defineConfig({
  plugins: [...astryxStylex(), react()],
});

```

The spread operator is required because `astryxStylex()` returns an array of plugins.

### Advanced Vite Configuration

```ts
// vite.config.ts
import {defineConfig} from 'vite';
import {astryxStylex} from '@astryxdesign/build/vite';

export default defineConfig({
  plugins: [
    ...astryxStylex({
      dev: true,
      libraryPattern: 'packages/core/',           // Custom library detection
      layers: {library: 'astryx-base', product: 'app'},  // Rename layers
      lightningcssTargets: {chrome: 120 << 16},  // Browser support
      stylexPrefix: 'astryx',                     // Base prefix for library
      stylexOverrides: {
        treeshakeCompensation: false,            // Disable tree-shake fix
      },
    }),
  ],
});

```

### Next.js Integration

```js
// next.config.mjs
import {withAstryx} from '@astryxdesign/build/next';

export default withAstryx({
  // Next.js-specific configuration
});

```

The `withAstryx` wrapper in the [Next.js integration](https://github.com/facebook/astryx/blob/main/packages/build/src/next.ts) applies the same plugin chain to webpack.

### Standalone PostCSS Configuration

```js
// postcss.config.js
const {postcss} = require('@astryxdesign/build');

module.exports = postcss(__dirname);

```

The `postcss()` helper in [[`config.js`](https://github.com/facebook/astryx/blob/main/config.js)](https://github.com/facebook/astryx/blob/main/packages/build/src/config.js) generates a complete configuration including StyleX compilation, layer injection, and optional LightningCSS.

## Key Source Files for Debugging

| File | Responsibility | Direct URL |
|------|---------------|------------|
| [`packages/build/src/vite.ts`](https://github.com/facebook/astryx/blob/main/packages/build/src/vite.ts) | Main Vite plugin, layer order plugin, split-layer middleware, config injection | [source](https://github.com/facebook/astryx/blob/main/packages/build/src/vite.ts) |
| [`packages/build/src/babel.js`](https://github.com/facebook/astryx/blob/main/packages/build/src/babel.js) | Babel wrapper with `classNamePrefix` switching logic | [source](https://github.com/facebook/astryx/blob/main/packages/build/src/babel.js) |
| [`packages/build/src/index.js`](https://github.com/facebook/astryx/blob/main/packages/build/src/index.js) | Public exports (`babel`, `postcss`, `astryxStylex`) | [source](https://github.com/facebook/astryx/blob/main/packages/build/src/index.js) |
| [`packages/build/src/config.js`](https://github.com/facebook/astryx/blob/main/packages/build/src/config.js) | PostCSS configuration builder | [source](https://github.com/facebook/astryx/blob/main/packages/build/src/config.js) |
| [`packages/build/README.md`](https://github.com/facebook/astryx/blob/main/packages/build/README.md) | Installation and usage documentation | [source](https://github.com/facebook/astryx/blob/main/packages/build/README.md) |

## Summary

- **`@astryxdesign/build` requires three coordinated plugins** — Vite, Babel, and PostCSS — for correct StyleX compilation with library/product style separation.
- **Class name collisions indicate missing Babel wrapper** — ensure `...require('@astryxdesign/build').babel` is in your Babel config.
- **Empty CSS indicates `optimizeDeps` interference** — the Vite plugin auto-excludes Astryx packages, but manual `optimizeDeps` configuration can override this.
- **Layer ordering problems indicate missing CSS layers** — verify the `astryx-css-layer-order` plugin injects the `@layer` declaration and the split-layer interceptor runs.
- **All configuration flows through [`vite.ts`](https://github.com/facebook/astryx/blob/main/vite.ts)** — use the `astryxStylex()` options object to customize patterns, layers, targets, and StyleX behavior directly.

## Frequently Asked Questions

### Why does my app show duplicate or conflicting class names?

The Babel wrapper in [[`babel.js`](https://github.com/facebook/astryx/blob/main/babel.js)](https://github.com/facebook/astryx/blob/main/packages/build/src/babel.js) applies different `classNamePrefix` values based on file location. If missing, both library and product code use the same prefix. Add `...require('@astryxdesign/build').babel` to your Babel plugins array to enable prefix separation.

### Can I use @astryxdesign/build without Vite?

Yes, but you must manually wire the three pieces. Use the Babel plugin directly for compilation, the PostCSS helper for CSS processing, and implement your own layer injection. The Vite plugin in [[`vite.ts`](https://github.com/facebook/astryx/blob/main/vite.ts)](https://github.com/facebook/astryx/blob/main/packages/build/src/vite.ts) serves as the reference implementation for coordination.

### How do I debug which layer my styles end up in?

Enable `dev: true` in `astryxStylex()` options to preserve readable class names. Inspect the generated CSS in `virtual:stylex.css` during development — library styles appear in `@layer astryx-base` blocks, product styles in `@layer product` blocks. Check that your `libraryPattern` regex correctly matches your folder structure.

### What browsers does the LightningCSS optimization target by default?

The default targets depend on your StyleX version and whether you provide `lightningcssTargets`. Without explicit targets, LightningCSS uses a conservative baseline. Specify modern targets as bit-shifted integers (e.g., `chrome: 120 << 16`) to enable native `light-dark()` and other modern features without polyfills.