gtk3: distinguish between first, last and only tabs

Change-Id: Ic69b84a3dd94ee25d5e660da152b1e776fa2b38e

vcl/unx/gtk3/gdi/gtk3salnativewidgets-gtk.cxx

@@ -956,7 +956,18 @@ bool GtkSalGraphics::drawNativeControl( ControlType nType, ControlPart nPart, co
     gtk_style_context_set_state(context, flags);
     if (nType == CTRL_TAB_ITEM)
     {
-        gtk_style_context_add_region(mpNoteBookStyle, GTK_STYLE_REGION_TAB, GTK_REGION_EVEN);
+
+        const TabitemValue& rTabitemValue = static_cast<const TabitemValue&>(aValue);
+
+        GtkRegionFlags eFlags(GTK_REGION_EVEN);
+        if (rTabitemValue.isFirst() && rTabitemValue.isLast())
+            eFlags = GTK_REGION_ONLY;
+        else if (rTabitemValue.isFirst())
+            eFlags = GTK_REGION_FIRST;
+        else if (rTabitemValue.isLast())
+            eFlags = GTK_REGION_LAST;
+
+        gtk_style_context_add_region(mpNoteBookStyle, GTK_STYLE_REGION_TAB, eFlags);
         gtk_style_context_add_class(context, GTK_STYLE_CLASS_TOP);
     }
     if (styleClass)