Added navigation to main menu options

Scripts/MainMenu.cs

@@ -14,6 +14,9 @@ public partial class MainMenu : CanvasLayer
 	[Export]
 	public Control SubMenuHolder { get; set; } = new Control();
 
+	[Export]
+	public Button DefaultSelectedButton { get; private set; }
+	
 	[Export]
 	public AudioStreamPlayer2D MusicPlayer { get; private set; }
 
@@ -36,6 +39,7 @@ public partial class MainMenu : CanvasLayer
 	// Called when the node enters the scene tree for the first time.
 	public override void _Ready()
 	{
+		DefaultSelectedButton.GrabFocus();
 	}
 
 	// Called every frame. 'delta' is the elapsed time since the previous frame.
@@ -103,6 +107,8 @@ public partial class MainMenu : CanvasLayer
 			{
 				MusicPlayer.Play();
 			}
+			
+			DefaultSelectedButton.GrabFocus();
 		};
 	}