fix header main widgets vertical align

src/app/browser/header/main.cpp

@@ -11,6 +11,10 @@ Main::Main()
         Gtk::Orientation::VERTICAL
     );
 
+    set_valign(
+        Gtk::Align::CENTER
+    );
+
     set_homogeneous(
         HOMOGENEOUS
     );

src/app/browser/header/main.hpp

@@ -3,6 +3,7 @@
 
 #include <glibmm/ustring.h>
 #include <gtkmm/box.h>
+#include <gtkmm/enums.h>
 #include <gtkmm/object.h>
 
 namespace app::browser::header