added class vbox-main and main- pannel in the css

hellofx/app/src/main/resources/client/style.css

@@ -1,7 +1,13 @@
-GridPane{
+.main-panel{
     -fx-background-color: #282C34;
 }
 
+.vbox-main{
+    -fx-background-color: #333333;
+    -fx-alignment: top-center;
+
+}
+
 Label{
     -fx-text-fill: white;
 }
@@ -14,4 +20,5 @@ Label{
     -fx-min-height: 40px;
     -fx-max-width: 40px;
     -fx-max-height: 40px;
-}
+}
+