widgets, themes: Define colors for GimpBlobEditor

The color for the nib handle is pulled from
the widget's background-color style.
However, this was not defined - so it was
always (0, 0, 0).
This patch adds a GimpBlobEditor CSS
class and defines the background and
border color for it to resolve the issue.

app/widgets/gimpblobeditor.c

@@ -103,6 +103,8 @@ gimp_blob_editor_class_init (GimpBlobEditorClass *klass)
                                                         -G_PI, G_PI, 0.0,
                                                         GIMP_PARAM_READWRITE |
                                                         G_PARAM_CONSTRUCT));
+
+  gtk_widget_class_set_css_name (widget_class, "GimpBlobEditor");
 }
 
 static void

themes/Default/common.css

@@ -126,6 +126,13 @@ combobox arrow, combobox button * {
   -gtk-icon-shadow: none;
 }
 
+/* Define colors so the nib handle appears in Gimp Ink Options */
+GimpBlobEditor {
+  color: @fg-color;
+  background-color: @bg-color;
+  border: 0.1em solid @fg-color;
+}
+
 /* Get rid of the outline around all tabs in the gimpcolordialog */
 GimpColorNotebook .frame {
   border-color: @bg-color;