codebrainz commented on this pull request.
void notebook_init(void)
{ + GtkWidget *btn = gtk_button_new_with_label("☰");
I think I've seen in some GNOME apps they use icon button with an icon like `view-list` or `view-more` or maybe some more semantically correct name for same icon. I guess the advantage of the icon is that it looks correct no matter which font or size being used (ex. in my browser here, it looks like an equal symbol).