GTK + program does not change the style

On Debian 9.8 with Gnome GTK +, the program does not change the style.

main.cpp

#include <gtk/gtk.h> void myStyleCss(void); void createWind(GtkWidget **window, gint width, gint height); void createGrid(GtkWidget **grid, GtkWidget **window, const gchar *name); void chngBkgrd(gpointer *data); int main(int argc, char *argv[]){ GtkWidget *window; GtkWidget *grid; GtkWidget *button; gtk_init(&argc, &argv); myStyleCss(); createWind(&window, 350, 250); createGrid(&grid, &window, "myGrid"); button = gtk_toggle_button_new_with_label("tgl_btn"); g_signal_connect (button, "toggled", G_CALLBACK(chngBkgrd),(gpointer *)button); gtk_grid_attach (GTK_GRID (grid), button, 0 , 0, 1, 1); gtk_widget_show_all(window); gtk_main(); } void myStyleCss(void){ GtkCssProvider *provider; GdkDisplay *display; GdkScreen *screen; provider = gtk_css_provider_new (); display = gdk_display_get_default (); screen = gdk_display_get_default_screen (display); gtk_style_context_add_provider_for_screen (screen, GTK_STYLE_PROVIDER(provider), GTK_STYLE_PROVIDER_PRIORITY_APPLICATION); const gchar *myCssFile = "style.css"; GError *error = 0; gtk_css_provider_load_from_file(provider, g_file_new_for_path(myCssFile), &error); g_object_unref (provider); } void createWind(GtkWidget **window, gint width, gint height){ *window = gtk_window_new(GTK_WINDOW_TOPLEVEL); gtk_window_set_title(GTK_WINDOW(*window), "MyApp"); gtk_window_set_default_size(GTK_WINDOW(*window), width, height); gtk_window_set_resizable (GTK_WINDOW(*window), TRUE); gtk_container_set_border_width(GTK_CONTAINER(*window), 5); g_signal_connect(*window, "destroy", G_CALLBACK(gtk_main_quit), NULL); } void createGrid(GtkWidget **grid, GtkWidget **window, const gchar *name){ *grid = gtk_grid_new (); gtk_grid_set_row_homogeneous(GTK_GRID(*grid), TRUE); gtk_grid_set_column_homogeneous(GTK_GRID(*grid), TRUE); gtk_widget_set_name(*grid, name); gtk_container_set_border_width(GTK_CONTAINER (*grid), 50); g_object_set (*grid, "margin", 0, NULL); gtk_container_add (GTK_CONTAINER (*window), *grid); } void chngBkgrd(gpointer *data){ if(gtk_toggle_button_get_active(GTK_TOGGLE_BUTTON(data))){ g_print("On\n"); } else{ g_print("Off\n"); } } 

style.css

 GtkWindow { background-color: red; color: cyan; border-width: 3px; border-color: blue; }; #myGrid { background-color: white; border-style: solid; border-width: 3px; border-radius: 15px; border-color: grey; }; #myChild { background-color: red; border-style: solid; border-width: 3px; border-radius: 15px; border-color: grey; }; #tgl_btn{ background-color: red; color: red; }; GtkButton { background-image: none; background-color: blue; }; GtkButton:active { background-color: #00FF00; }; GtkButton:checked{ background-color: #000000; };