I am using glade 3.40.0 to edit a GTK+ GUI for a python app, I understand the glade tool is not currently maintained. I have added a GtkEntry object to my existing GUI, and I want to specify the font and the colors for the background and foreground. But I have discovered that unlike GtkLabel objects, glade does not provide the option to "Edit Attributes" of GtkEntry. Instead, there is a "Style Classes" box.
I don't know what to enter in that box. My searching leads me to expect that I must write a css style sheet file, load it, and make it available to glade and my app. But I have not found any documentation on how to do those steps. What do I do?