[gtk] colorplane: Set a css name

[Matthias Clasen <matthiasc src gnome org>]

commit 9f252f0cebfaab7cec24803495e2423c765b8563
Author: Matthias Clasen <mclasen redhat com>
Date:   Thu Apr 9 14:10:23 2020 -0400

    colorplane: Set a css name
    
    Every widget should have one.

 gtk/gtkcolorplane.c | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/gtk/gtkcolorplane.c b/gtk/gtkcolorplane.c
index bbe7ac0f2d..2c4ae692f2 100644
--- a/gtk/gtkcolorplane.c
+++ b/gtk/gtkcolorplane.c
@@ -545,6 +545,8 @@ gtk_color_plane_class_init (GtkColorPlaneClass *class)
                                                        GTK_TYPE_ADJUSTMENT,
                                                        GTK_PARAM_WRITABLE |
                                                        G_PARAM_CONSTRUCT_ONLY));
+
+  gtk_widget_class_set_css_name (widget_class, "plane");
 }
 
 GtkWidget *