diff --git a/gnucash/gnome-utils/dialog-utils.c b/gnucash/gnome-utils/dialog-utils.c
index 9d9ef32cf6..49f699ba70 100644
--- a/gnucash/gnome-utils/dialog-utils.c
+++ b/gnucash/gnome-utils/dialog-utils.c
@@ -70,13 +70,13 @@ gnc_set_label_color(GtkWidget *label, gnc_numeric value)
 
     if (deficit)
     {
-        gnc_widget_style_context_remove_class (GTK_WIDGET(label), "default-color");
-        gnc_widget_style_context_add_class (GTK_WIDGET(label), "negative-numbers");
+        gnc_widget_style_context_remove_class (GTK_WIDGET(label), "gnc-class-default-color");
+        gnc_widget_style_context_add_class (GTK_WIDGET(label), "gnc-class-negative-numbers");
     }
     else
     {
-        gnc_widget_style_context_remove_class (GTK_WIDGET(label), "negative-numbers");
-        gnc_widget_style_context_add_class (GTK_WIDGET(label), "default-color");
+        gnc_widget_style_context_remove_class (GTK_WIDGET(label), "gnc-class-negative-numbers");
+        gnc_widget_style_context_add_class (GTK_WIDGET(label), "gnc-class-default-color");
     }
 }
 
@@ -889,7 +889,7 @@ gnc_cost_policy_select_new (void)
     return cost_policy_widget;
 }
 
-/* This function returns a string for the CSS 'negative-numbers' class,
+/* This function returns a string for the CSS 'gnc-class-negative-numbers' class,
  * the returned string must be freed
  */
 gchar*
@@ -898,7 +898,7 @@ gnc_get_negative_color (void)
     GdkRGBA color;
     GtkWidget *label = gtk_label_new ("Color");
     GtkStyleContext *context = gtk_widget_get_style_context (GTK_WIDGET(label));
-    gtk_style_context_add_class (context, "negative-numbers");
+    gtk_style_context_add_class (context, "gnc-class-negative-numbers");
     gtk_style_context_get_color (context, GTK_STATE_FLAG_NORMAL, &color);
 
     return gdk_rgba_to_string (&color);
diff --git a/gnucash/gnome-utils/dialog-utils.h b/gnucash/gnome-utils/dialog-utils.h
index 1c9c56ef01..f62c92d348 100644
--- a/gnucash/gnome-utils/dialog-utils.h
+++ b/gnucash/gnome-utils/dialog-utils.h
@@ -161,7 +161,7 @@ gboolean gnc_new_book_option_display (GtkWidget *parent);
 GtkWidget *
 gnc_cost_policy_select_new (void);
 
-/** This function returns the color string for the CSS 'negative-numbers' class,
+/** This function returns the color string for the CSS 'gnc-class-negative-numbers' class,
  *  the returned value must be freed.
  */
 gchar* gnc_get_negative_color (void);
diff --git a/gnucash/gnome-utils/window-main-summarybar.c b/gnucash/gnome-utils/window-main-summarybar.c
index 14b992835e..ca1369ee6b 100644
--- a/gnucash/gnome-utils/window-main-summarybar.c
+++ b/gnucash/gnome-utils/window-main-summarybar.c
@@ -450,7 +450,7 @@ get_negative_color_str (void)
     gchar *color_str;
     GtkWidget *label = gtk_label_new ("Color");
     GtkStyleContext *context = gtk_widget_get_style_context (GTK_WIDGET(label));
-    gtk_style_context_add_class (context, "negative-numbers");
+    gtk_style_context_add_class (context, "gnc-class-negative-numbers");
     gtk_style_context_get_color (context, GTK_STATE_FLAG_NORMAL, &color);
     rgba = gdk_rgba_copy (&color);
 
diff --git a/gnucash/gnucash-310.css b/gnucash/gnucash-310.css
index 692919bdc3..30c9bdb2af 100644
--- a/gnucash/gnucash-310.css
+++ b/gnucash/gnucash-310.css
@@ -4,11 +4,11 @@
 
 
 /* Negative value label colors */
-.default-color {
+.gnc-class-default-color {
   color: @default-color;
 }
 
-.negative-numbers {
+.gnc-class-negative-numbers {
   color: @negative-numbers;
 }
 
diff --git a/gnucash/gnucash-320.css b/gnucash/gnucash-320.css
index 561de812d7..9439430c68 100644
--- a/gnucash/gnucash-320.css
+++ b/gnucash/gnucash-320.css
@@ -4,11 +4,11 @@
 
 
 /* Negative value label colors */
-.default-color {
+.gnc-class-default-color {
   color: @default-color;
 }
 
-.negative-numbers {
+.gnc-class-negative-numbers {
   color: @negative-numbers;
 }
 
diff --git a/gnucash/register/register-gnome/gnucash-sheet.c b/gnucash/register/register-gnome/gnucash-sheet.c
index 36bd9c6525..55c3737973 100644
--- a/gnucash/register/register-gnome/gnucash-sheet.c
+++ b/gnucash/register/register-gnome/gnucash-sheet.c
@@ -2525,7 +2525,7 @@ gnucash_get_style_classes (GnucashSheet *sheet, GtkStyleContext *stylectxt,
 
     if (field_type >= COLOR_NEGATIVE) // Require a Negative fg color
     {
-        gtk_style_context_add_class (stylectxt, "negative-numbers");
+        gtk_style_context_add_class (stylectxt, "gnc-class-negative-numbers");
         field_type -= COLOR_NEGATIVE;
     }
     else