How to Use Sass with Sage

Remove Tailwind CSS dependencies: npm uninstall -D @tailwindcss/vite tailwindcss

Delete the contents of resources/css/app.css and resources/css/editor.css.

Add the sass extension:

npm install -D sass

In the resources/css directory, rename app.css to app.scss and rename editor.css to editor.scss.

app.css    -> app.scss
editor.css -> editor.scss

Modify vite.config.js to remove the Tailwind plugin, reference the new file extensions, and disable the Tailwind CSS theme.json generation:

 import { defineConfig } from 'vite'
-import tailwindcss from '@tailwindcss/vite';
 import laravel from 'laravel-vite-plugin'
 import { wordpressPlugin, wordpressThemeJson } from '@roots/vite-plugin';

 export default defineConfig({
   base: '/app/themes/sage/public/build/',
   plugins: [
-    tailwindcss(),
     laravel({
       input: [
-        'resources/css/app.css',
+        'resources/css/app.scss',
         'resources/js/app.js',
-        'resources/css/editor.css',
+        'resources/css/editor.scss',
         'resources/js/editor.js',
       ],

     wordpressThemeJson({
-      disableTailwindColors: false,
-      disableTailwindFonts: false,
-      disableTailwindFontSizes: false,
+      disableTailwindColors: true,
+      disableTailwindFonts: true,
+      disableTailwindFontSizes: true,
     }),
   ],

Modify the @vite() directive in resourves/views/layouts/app.blade.php to use app.scss instead of app.css:

-    @vite(['resources/css/app.css', 'resources/js/app.js'])
+    @vite(['resources/css/app.scss', 'resources/js/app.js'])

Modify the block_editor_settings_all filter in app/setup.php to use editor.scss instead of editor.css;

add_filter('block_editor_settings_all', function ($settings) {
-    $style = Vite::asset('resources/css/editor.css');
+    $style = Vite::asset('resources/css/editor.scss');

    $settings['styles'][] = [
        'css' => Vite::isRunningHot()
            ? "@import url('{$style}')"
-           : Vite::content('resources/css/editor.css'),
+           : Vite::content('resources/css/editor.scss'),
    ];

    return $settings;
});