diff --git a/pkg-config/READMD.md b/pkg-config/READMD.md
new file mode 100644
index 0000000..b0b2876
--- /dev/null
+++ b/pkg-config/READMD.md
@@ -0,0 +1,47 @@
+## `pkg-config`
+
+```sh
+sudo apt install -y libgtk-3-dev build-essential pkg-config
+pkg-config --cflags --libs gtk+-3.0
+
+tee gtk_dark_test.c << 'EOF'
+#include <gtk/gtk.h>
+
+static void activate(GtkApplication* app, gpointer user_data) {
+    GtkWidget *window;
+    GtkWidget *button;
+    GtkWidget *box;
+
+    window = gtk_application_window_new(app);
+    gtk_window_set_title(GTK_WINDOW(window), "Dark Theme Test");
+    gtk_window_set_default_size(GTK_WINDOW(window), 200, 200);
+
+    box = gtk_box_new(GTK_ORIENTATION_VERTICAL, 0);
+    gtk_widget_set_halign(box, GTK_ALIGN_CENTER);
+    gtk_widget_set_valign(box, GTK_ALIGN_CENTER);
+
+    button = gtk_button_new_with_label("Hello World");
+    g_signal_connect_swapped(button, "clicked", G_CALLBACK(gtk_window_close), window);
+
+    gtk_container_add(GTK_CONTAINER(window), box);
+    gtk_container_add(GTK_CONTAINER(box), button);
+
+    gtk_widget_show_all(window);
+}
+
+int main(int argc, char **argv) {
+    GtkApplication *app;
+    int status;
+
+    app = gtk_application_new("org.gtk.example", G_APPLICATION_DEFAULT_FLAGS);
+    g_signal_connect(app, "activate", G_CALLBACK(activate), NULL);
+    status = g_application_run(G_APPLICATION(app), argc, argv);
+    g_object_unref(app);
+
+    return status;
+}
+EOF
+gcc -o gtk_dark_test gtk_dark_test.c `pkg-config --cflags --libs gtk+-3.0`
+export GTK_THEME=Adwaita:dark
+./gtk_dark_test
+```