How to apply style using GtkSourceView library - gtk3

Question

I'm trying to style a GtkSourceView object in particular I'd like to change the color of line numbers. I'm reading Style Scheme Definition Reference: GtkSourceView 4 Reference Manual. I'm able to change text but not line-numbers. The document says:
line-numbers : Text and background colors for the left margin, on which line numbers are drawn.
This is the source:
#include <gtk/gtk.h>
#include <gtksourceview/gtksource.h>
int main (int argc,
char *argv[])
{
GtkWidget *window, *scrolled_win, *textview;
GtkWidget *vbox, *menubar, *fileMenu, *fileMi, *quit_item;
gtk_init (&argc, &argv);
window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
gtk_window_maximize(GTK_WINDOW (window));
vbox = gtk_box_new(GTK_ORIENTATION_VERTICAL, 12);
gtk_container_add(GTK_CONTAINER(window), vbox);
gtk_window_set_title (GTK_WINDOW (window), "Text Views");
gtk_container_set_border_width (GTK_CONTAINER (window), 10);
textview = gtk_source_view_new();
menubar = gtk_menu_bar_new();
fileMenu = gtk_menu_new();
fileMi = gtk_menu_item_new_with_label("File");
quit_item = gtk_menu_item_new_with_label("Quit");
gtk_widget_set_hexpand(textview, TRUE);
gtk_widget_set_vexpand(textview, TRUE);
GtkCssProvider *provider = gtk_css_provider_new ();
gtk_css_provider_load_from_path (provider,
"gtk-widgets.css", NULL);
GtkStyleContext *context;
context = gtk_widget_get_style_context(textview);
gtk_style_context_add_provider (context,
GTK_STYLE_PROVIDER(provider),
GTK_STYLE_PROVIDER_PRIORITY_USER);
gtk_menu_item_set_submenu(GTK_MENU_ITEM(fileMi), fileMenu);
gtk_menu_shell_append(GTK_MENU_SHELL(fileMenu), quit_item);
gtk_menu_shell_append(GTK_MENU_SHELL(menubar), fileMi);
gtk_box_pack_start(GTK_BOX(vbox), menubar, FALSE, FALSE, 0);
scrolled_win = gtk_scrolled_window_new (NULL, NULL);
gtk_container_add(GTK_CONTAINER(vbox), scrolled_win);
gtk_container_add (GTK_CONTAINER (scrolled_win), textview);
gtk_source_view_set_show_line_numbers (GTK_SOURCE_VIEW(textview), TRUE);
gtk_widget_show_all (window);
g_signal_connect(G_OBJECT(window), "destroy",
G_CALLBACK(gtk_main_quit), NULL);
g_signal_connect(G_OBJECT(quit_item), "activate",
G_CALLBACK(gtk_main_quit), NULL);
gtk_main();
return 0;
}
This is the CSS file:
text {
background-color: #002b36;
color: #c7a21d;
}
line-numbers {
background-color: red;
color:red;
}
current-line-number {
background-color: red;
color:red;
}
selection{
color:yellow;
}
What am I doing wrong?

Answer 1

The API has a way to access the default styles like this:
manager = GtkSource.StyleSchemeManager().get_default()
print (manager.get_scheme_ids())
>['classic', 'cobalt', 'kate', 'oblivion', 'solarized-dark', 'solarized-light', 'tango']
scheme = manager.get_scheme("oblivion")
buffer.set_style_scheme(scheme)
An example for good measure:
import gi
gi.require_version('Gtk', '3.0')
from gi.repository import Gtk as gtk
from gi.repository import Gdk as gdk
from gi.repository import GtkSource as gtksource
from gi.repository import Pango
view = gtksource.View()
view.modify_font(Pango.FontDescription('monospace 11'))
view.set_show_line_numbers(True)
view.set_show_line_marks(True)
buffer = view.get_buffer()
filename = "treeview.py"
txt = open(filename).read()
buffer.set_text(txt)
# set language, syntax highlighting
lm = gtksource.LanguageManager.new()
lang = lm.guess_language(filename)
buffer.set_highlight_syntax(True)
buffer.set_language(lang)
buffer.create_tag("invisible",invisible=True)
manager = gtksource.StyleSchemeManager().get_default()
scheme = manager.get_scheme("monokai")
buffer.set_style_scheme(scheme)
window = gtk.Window()
window.connect("destroy", gtk.main_quit)
window.add(view)
window.show_all()
gtk.main()
From there you should be able use the guide to apply custom themes, change colours of certain elements, etc...