diff --git a/src/Entity/App.php b/src/Entity/App.php
index fc36e800..57688534 100644
--- a/src/Entity/App.php
+++ b/src/Entity/App.php
@@ -17,6 +17,22 @@ class App
         // Init config
         $this->config = \Yggverse\Yoda\Model\File::getConfig()->app; // @TODO
 
+        // Init theme
+        $css = new \GtkCssProvider();
+
+        $css->load_from_data(
+            \Yggverse\Yoda\Model\File::getTheme(
+                $this->config->theme
+            )
+        );
+
+        $style = new \GtkStyleContext();
+
+        $style->add_provider_for_screen(
+            $css,
+            600
+        );
+
         // Init window
         $this->window = new \GtkWindow;
 
diff --git a/src/Theme/Default.css b/src/Theme/Default.css
index e6f46b06..ed4b5e90 100644
--- a/src/Theme/Default.css
+++ b/src/Theme/Default.css
@@ -1,3 +1 @@
-#boxMenu {}
-#boxNavigation {}
-#boxTab {}
\ No newline at end of file
+/* Custom CSS */
\ No newline at end of file