Add tailwind integration new nesting option (withastro#5974)

Co-authored-by: Sarah Rainsberger <[email protected]>
Co-authored-by: voxel!() <[email protected]>

src/content/docs/en/guides/integrations-guide/tailwind.mdx

@@ -159,6 +159,25 @@ export default defineConfig({
 
 You can now [import your own `base.css` as a local stylesheet](/en/guides/styling/#import-a-local-stylesheet).
 
+#### nesting
+
+Set `true` to apply the [`tailwindcss/nesting` PostCSS plugin](https://tailwindcss.com/docs/using-with-preprocessors#nesting) so you can write nested CSS declarations alongside Tailwind's syntax. This option is `false` by default.
+
+```js ins="nesting: true"
+// astro.config.mjs
+import { defineConfig } from 'astro/config';
+
+export default defineConfig({
+  integrations: [
+    tailwind({
+      // Example: Allow writing nested CSS declarations
+      // alongside Tailwind's syntax
+      nesting: true,
+    }),
+  ],
+});
+```
+
 ## Examples
 
 * The [Astro Tailwind Starter](https://github.com/withastro/astro/tree/latest/examples/with-tailwindcss?on=github) gets you up and running with a base for your project that uses Tailwind for styling