app/widgets, themes: Show Sample Point indexes in Default theme

The Default box.vertical style covers up
the Sample Point indexes that are drawn
with Cairo. This patch adds a style for the
GimpSamplePointEditor that sets its inner
box.vertical to transparent in order to
to make the indexes visible.

app/widgets/gimpsamplepointeditor.c

@@ -119,6 +119,8 @@ gimp_sample_point_editor_class_init (GimpSamplePointEditorClass *klass)
                                                          TRUE,
                                                          GIMP_PARAM_READWRITE |
                                                          G_PARAM_CONSTRUCT));
+
+  gtk_widget_class_set_css_name (widget_class, "GimpSamplePointEditor");
 }
 
 static void

themes/Default/common.css

@@ -309,8 +309,7 @@ scrollbar slider {
   border: 2px solid @border-color;
 }
 
-scrolledwindow
-{
+scrolledwindow {
   border-color: @edge-border-color;
 }
 
@@ -329,6 +328,11 @@ GimpRuler {
   background-color: @ruler-color;
 }
 
+/* Make sure the sample point numbers are visible */
+GimpSamplePointEditor box.vertical {
+  background-color: transparent;
+}
+
 entry {
   background-color: @extreme-bg-color;
   color: @fg-color;