feat: stabilize css.preprocessorMaxWorkers and default to true (#19992)

Author: sapphi-red

docs/config/shared-options.md

@@ -278,11 +278,12 @@ export default defineConfig({
 
 ## css.preprocessorMaxWorkers
 
-- **Experimental:** [Give Feedback](https://github.com/vitejs/vite/discussions/15835)
 - **Type:** `number | true`
-- **Default:** `0` (does not create any workers and run in the main thread)
+- **Default:** `true`
+
+Specifies the maximum number of threads CSS preprocessors can use. `true` means up to the number of CPUs minus 1. When set to `0`, Vite will not create any workers and will run the preprocessors in the main thread.
 
-If this option is set, CSS preprocessors will run in workers when possible. `true` means the number of CPUs minus 1.
+Depending on the preprocessor options, Vite may run the preprocessors on the main thread even if this option is not set to `0`.
 
 ## css.devSourcemap
 

packages/vite/src/node/plugins/css.ts

@@ -143,8 +143,7 @@ export interface CSSOptions {
    * If this option is set, preprocessors will run in workers when possible.
    * `true` means the number of CPUs minus 1.
    *
-   * @default 0
-   * @experimental
+   * @default true
    */
   preprocessorMaxWorkers?: number | true
   postcss?:
@@ -198,8 +197,7 @@ export const cssConfigDefaults = Object.freeze({
   transformer: 'postcss',
   // modules
   // preprocessorOptions
-  /** @experimental */
-  preprocessorMaxWorkers: 0,
+  preprocessorMaxWorkers: true,
   // postcss
   /** @experimental */
   devSourcemap: false,