diff --git a/TODO (next version).txt b/TODO (next version).txt
index 051aea6..27e58b2 100644
--- a/TODO (next version).txt	
+++ b/TODO (next version).txt	
@@ -66,6 +66,8 @@ http://css.mammouthland.net/feuille-de-style-css-debutant.php
 https://docs.gtk.org/gtk3/method.Widget.set_name.html
 Widgets can be named, which allows you to refer to them from a CSS file.
 https://docs.w3cub.com/gtk~4.0/gtkstylecontext.html
+https://docs.gtk.org/gtk3/class.StyleContext.html
+GtkStyleContext is an object that stores styling information affecting a widget defined by GtkWidgetPath.
 
 on peut déclarer les styles à différents endroits, et selon ces endroits ils seront plus ou moins prioritaires.
 On obtient donc une cascade de styles. Par priorité décroissante :
diff --git a/src/ui/contain.c b/src/ui/contain.c
index a001284..03922cd 100644
--- a/src/ui/contain.c
+++ b/src/ui/contain.c
@@ -178,10 +178,17 @@ void window_bar(GtkWindow *window, char *title){
 }
 
 void experimental_activate_00 (GtkApplication *app, GtkWindow *window) {
-  window_bar (window, "E coli   (with permission from David S. Goodsell, 2009)");
+//  window_bar (window, "E coli   (with permission from David S. Goodsell, 2009)");
+  GtkWidget *my_header_bar = gtk_header_bar_new ();
+  gtk_header_bar_set_title_widget (my_header_bar, GTK_WIDGET (gtk_label_new ("E coli   (with permission from David S. Goodsell, 2009)")));
+  GtkWidget *run_edit = gtk_toggle_button_new ();
+  gtk_button_set_icon_name (run_edit, "system-run-symbolic");
+  gtk_header_bar_pack_start (my_header_bar, run_edit);
+  gtk_window_set_titlebar (window, my_header_bar);
+
 
   GtkNotebook *run_notebook = GTK_NOTEBOOK (gtk_notebook_new());
-  gtk_notebook_set_tab_pos (run_notebook, GTK_POS_TOP);  //   GTK_POS_LEFT
+//  gtk_notebook_set_tab_pos (run_notebook, GTK_POS_TOP);  //   TOP par défaut ?  possible : GTK_POS_LEFT
 
   gtk_notebook_append_page (run_notebook, get_run_space_page_new(),   gtk_label_new ("space"));
   gtk_notebook_append_page (run_notebook, get_run_rules_page_new(),   gtk_label_new ("rules"));
@@ -191,7 +198,7 @@ void experimental_activate_00 (GtkApplication *app, GtkWindow *window) {
   gtk_notebook_append_page (run_notebook, get_run_help_page_new(),    gtk_label_new ("help"));
 
   GtkNotebook *edit_notebook = GTK_NOTEBOOK (gtk_notebook_new());
-  gtk_notebook_set_tab_pos (edit_notebook, GTK_POS_TOP);  //   GTK_POS_RIGHT
+//  gtk_notebook_set_tab_pos (edit_notebook, GTK_POS_TOP);   //   TOP par défaut,  I presume
 
   gtk_notebook_append_page (edit_notebook, get_edit_space_page_new(),   gtk_label_new ("space"));
   gtk_notebook_append_page (edit_notebook, get_edit_rules_page_new(),   gtk_label_new ("rules"));
@@ -207,7 +214,7 @@ void experimental_activate_00 (GtkApplication *app, GtkWindow *window) {
   gtk_paned_set_position (GTK_PANED (run_xor_edit_horizontal_pane), W_IMAGE + 350); // '350' : AD HOC
   gtk_window_set_child (window, GTK_WIDGET (run_xor_edit_horizontal_pane));
 
-  gtk_notebook_set_current_page (run_notebook, 1);  //    @see  hot.c   2024-05-11  (line 68)
-  gtk_notebook_set_current_page (edit_notebook, 1);  //    @see  hot.c   2024-05-11  (line 68)
+  gtk_notebook_set_current_page (run_notebook, 0);  //    @see  tree.c   2024-05-11  (line 68)
+  gtk_notebook_set_current_page (edit_notebook, 1);  //    @see  tree.c   2024-05-11  (line 68)
 }
 
diff --git a/src/ui/display.c b/src/ui/display.c
index 7106fd3..d1ac1b1 100644
--- a/src/ui/display.c
+++ b/src/ui/display.c
@@ -93,12 +93,16 @@ static GtkWidget *get_scroll_speed(){
   gtk_widget_set_size_request (GTK_WIDGET (scroll_speed), 120, 2);
 //  gtk_scale_set_has_origin (GTK_SCALE (scroll_speed), TRUE);
 //  gtk_scale_set_draw_value (GTK_SCALE (scroll_speed), TRUE);
-//  void value_changed (  GtkRange* self,  gpointer user_data)
+//  void value_changed (  GtkRange* self,  gpointer user_data);
+
+// 2024-05-28  essais
   const gchar *new_name = "new_name"; gtk_widget_set_name (scroll_speed, new_name);
 //  const GtkWidgetPath* gtk_style_context_get_path (GtkStyleContext* context);
-//
+//  GtkStyleContext *my_context = gtk_style_context_new ();
   gtk_style_context_set_state (gtk_widget_get_style_context (scroll_speed), 100);
-  printf("display.get_scroll_speed() gtk_style_context_get_state (gtk_widget_get_style_context (scroll_speed)) = %d\n", gtk_style_context_get_state (gtk_widget_get_style_context (scroll_speed)));
+  if (0) printf("display.get_scroll_speed() gtk_style_context_get_state (gtk_widget_get_style_context (scroll_speed)) = %d\n",\
+          gtk_style_context_get_state (gtk_widget_get_style_context (scroll_speed)));
+
   return scroll_speed;
 }
 
@@ -119,9 +123,9 @@ static GtkBox *get_DO_SPEED_box(){
 GtkBox *get_RUN_STOP_box(){
   GtkBox *RUN_STOP_box = GTK_BOX(gtk_box_new (GTK_ORIENTATION_HORIZONTAL, 20));
   gtk_box_append (RUN_STOP_box, GTK_WIDGET (get_UNDO_SPEED_box()));
-  gtk_box_append (RUN_STOP_box, GTK_WIDGET(gtk_label_new ("           STEP\n(show active rule) ")));
+  gtk_box_append (RUN_STOP_box, GTK_WIDGET (gtk_label_new ("           STEP\n(show active rule) ")));
   gtk_box_append (RUN_STOP_box, GTK_WIDGET (get_DO_SPEED_box()));
-  gtk_box_append (RUN_STOP_box, GTK_WIDGET(gtk_label_new ("      R U N\n     S T O P")));
+  gtk_box_append (RUN_STOP_box, GTK_WIDGET (gtk_label_new ("      R U N\n     S T O P")));
   return RUN_STOP_box;
 }
 //------------------------------------------------------------------------------