GtkSpinButton: should use "decrement" or "down" rather than "remove"
https://gitlab.gnome.org/GNOME/gtk/blob/master/gtk/gtkspinbutton.c#L876
priv->down_button = gtk_button_new_from_icon_name ("list-remove-symbolic");
In the theme I'm using, the icon that looks like "(X)" is assigned to "list-remove-symbolic". Therefore, I feel something strange about the appearance of GtkSpinButton.
Can you change the name of the icon?