Whitelist some CSS

gatsby-config.js

@@ -45,7 +45,13 @@ module.exports = {
     },
     'gatsby-plugin-sharp',
     'gatsby-transformer-sharp',
-    'gatsby-plugin-purgecss',
+    {
+      resolve: 'gatsby-plugin-purgecss',
+      options: {
+        printRejected: true,
+        whitelistPatterns: [/^(.*)-content(.*)/, /^event-grouped-by-(.*)/],
+      },
+    },
     'gatsby-plugin-netlify', // make sure to keep it last in the array
   ],
 }