Enable the 'apply complex classes' feature

Enable the experimental feature to use `@apply` with complex classes
including interactive states. I tried this on the Rebuilding Symfony
demo project and it worked well.

This would mean that I could refactor some of my existing styles on this
project.

References #190

web/themes/custom/opdavies/tailwind.config.js

@@ -93,5 +93,8 @@ module.exports = {
     borderStyle: [...variants.borderStyle, 'hover', 'focus'],
     borderWidth: [...variants.borderWidth, 'hover', 'focus'],
     margin: [...variants.margin, 'first', 'last', 'odd', 'even'],
+  },
+  experimental: {
+    applyComplexClasses: true
   }
 }