GUI: Restore bolding of active sheet tab

NEWS

@@ -7,6 +7,7 @@ Morten:
 	* Many improvements to vertical toolbars.
 	* Install appdata file in new location [#612]
 	* Allow styling of cell extension indicators.
+	* Restore bolding of active sheet tab.
 
 --------------------------------------------------------------------------
 Gnumeric 1.12.51

src/dialogs/wbcg.ui

 <?xml version="1.0" encoding="UTF-8"?>
-<!-- Generated with glade 3.16.1 -->
+<!-- Generated with glade 3.22.2 -->
 <interface>
   <requires lib="gtk+" version="3.8"/>
   <object class="GtkWindow" id="toplevel">
@@ -192,6 +192,9 @@
                         <child type="tab">
                           <placeholder/>
                         </child>
+                        <style>
+                          <class name="sheets"/>
+                        </style>
                       </object>
                       <packing>
                         <property name="expand">True</property>

src/gnumeric.css

@@ -127,14 +127,14 @@ GnmItemBar:hover {
 /* ------------------------------------------------------------------------- */
 /* This GtkDrawingArea is the select-all button above the row buttons.  */
 
-GtkDrawingArea.button.all {
+GtkDrawingArea.button.all, widget.button.all {
 }
 
 /* ------------------------------------------------------------------------- */
 
 /* GnmNotebook is a fake notebook holding just the sheet tabs area */
 
-GnmNotebook {
+GnmNotebook, notebook.buttons {
   padding-top: 0;
   padding-bottom: 0;
 }
@@ -190,7 +190,8 @@ GocItem.object-size.rubber-band {
 /* ------------------------------------------------------------------------- */
 /* GnmNotebookButton is the sheet name buttons used to select sheets.  */
 
-GnmNotebookButton:active {
+GnmNotebookButton:active,
+notebook.buttons tab label {
   font-weight: bold;
 }
 
@@ -229,12 +230,12 @@ button:hover.itembar, button:hover.itembar * {
 
 
 /* Small padding between and around toolbars, but not double between */
-box > box > toolbar {
+box > box > toolbar.horizontal {
     padding-top: 1pt;
     padding-bottom: 0pt;
 }
 
-box > box:last-child > toolbar {
+box > box:last-child > toolbar.horizontal {
     padding-top: 1pt;
     padding-bottom: 1pt;
 }

src/wbc-gtk.c

@@ -975,11 +975,14 @@ static void
 wbc_gtk_create_notebook_area (WBCGtk *wbcg)
 {
 	GtkWidget *placeholder;
+	GtkStyleContext *context;
 
 	wbcg->bnotebook = g_object_new (GNM_NOTEBOOK_TYPE,
 					"can-focus", FALSE,
 					NULL);
 	g_object_ref (wbcg->bnotebook);
+	context = gtk_widget_get_style_context (GTK_WIDGET (wbcg->bnotebook));
+	gtk_style_context_add_class (context, "buttons");
 
 	g_signal_connect_after (G_OBJECT (wbcg->bnotebook),
 		"switch_page",