diff --git a/rsbuild/stylex/README.md b/rsbuild/stylex/README.md
index a4ccee83..4123fce0 100644
--- a/rsbuild/stylex/README.md
+++ b/rsbuild/stylex/README.md
@@ -2,7 +2,9 @@
 
 Minimal example of using [StyleX](https://stylexjs.com/) with Rsbuild via the official [`@stylexjs/unplugin`](https://stylexjs.com/docs/learn/installation/rspack/) adapter.
 
-The plugin compiles StyleX at build time and appends the generated CSS to the stylesheet emitted by Rsbuild's `CssExtractRspackPlugin` (fed by `src/index.css`). StyleX styles therefore stay in the normal CSS asset pipeline with content-hashed filenames, instead of a separate hardcoded `/stylex.css` link.
+During development, `runtimeInjection` injects StyleX styles at runtime so style changes apply through HMR without a page refresh.
+
+In production, runtime injection is disabled. The plugin compiles StyleX at build time and appends the generated CSS to the stylesheet emitted by Rsbuild's `CssExtractRspackPlugin` (fed by `src/index.css`), producing content-hashed CSS filenames instead of a separate hardcoded `/stylex.css` link.
 
 This example uses `stylex.webpack()` (not `stylex.rspack()`) because `@stylexjs/unplugin` currently attaches CSS injection through the webpack-compatible hook; Rspack still runs that hook for plugins registered via `tools.rspack.plugins`.
 
diff --git a/rsbuild/stylex/rsbuild.config.ts b/rsbuild/stylex/rsbuild.config.ts
index a54d0883..1d2434af 100644
--- a/rsbuild/stylex/rsbuild.config.ts
+++ b/rsbuild/stylex/rsbuild.config.ts
@@ -16,6 +16,8 @@ export default defineConfig({
         // webpack-compatible plugins. The rspack() entry only runs transform.
         stylex.webpack({
           useCSSLayers: true,
+          // Inject styles during development so they update with HMR.
+          runtimeInjection: process.env.NODE_ENV === 'development',
         }),
       ],
     },