Add config to set default values

src/DependencyInjection/Configuration.php

@@ -20,6 +20,21 @@ class Configuration implements ConfigurationInterface
 
     private function addValidationRules(ArrayNodeDefinition $rootNode): void
     {
+        // I've split the tree up like this because Intelephense was crying.
+        // Plus I think it's a little easier to read.
+
+        $rootNode
+            ->children()
+                ->arrayNode('default')
+                    ->addDefaultsIfNotSet()
+                    ->children()
+                        ->scalarNode('colour')->defaultValue('primary')->end()
+                        ->integerNode('size')->defaultValue(32)->end()
+                    ->end()
+                ->end()
+            ->end()
+        ;
+
         $rootNode
             ->children()
                 ->arrayNode('directories')
@@ -34,6 +49,11 @@ class Configuration implements ConfigurationInterface
                         ->end()
                     ->end()
                 ->end()
+            ->end()
+        ;
+
+        $rootNode
+            ->children()
                 ->arrayNode('colours')
                     ->validate()
                         ->ifEmpty()