Test adding a variable via preprocessing

web/themes/contrib/tailwindcss/tailwindcss.theme

@@ -5,6 +5,13 @@
  * Functions to support theming in the Tailwind CSS theme.
  */
 
+/**
+ * Implements hook_preprocess_HOOK().
+ */
+function tailwindcss_preprocess_html(&$variables) {
+  $variables['attributes']['class'][] = 'tw-bg-red-200';
+}
+
 /**
  * Implements hook_preprocess_HOOK().
  */

web/themes/contrib/tailwindcss/webpack.mix.js

@@ -7,5 +7,6 @@ mix.postCss('src/main.css', 'dist', [
 ])
 .purgeCss({
   folders: ['templates'],
-  extensions: ['html', 'twig']
+  extensions: ['html', 'twig'],
+  whitelistPatterns: [/tw-bg-red-200/]
 })