how can I get underlined text using gtk4 css in C?

Question

This is the relevant part of the code:

 btn1 = gtk_button_new_with_label("one");
 gtk_grid_attach (GTK_GRID (grid_ptr), btn1, 0, 1, 1, 1);
 gtk_widget_set_name ( btn1, "btn1");
   
 GtkCssProvider *prvdr = gtk_css_provider_new ();
 GtkStyleContext *cntxt = gtk_widget_get_style_context ( btn1 );
    
 gtk_css_provider_load_from_data (prvdr, "button#btn1 { text-decoration: underline white;}", -1);
 gtk_style_context_add_provider (cntxt, GTK_STYLE_PROVIDER (prvdr), GTK_STYLE_PROVIDER_PRIORITY_APPLICATION);

It compiles without any issues, and runs without errors or warnings, but nothing gets underlined.

I have also tried these with the same result: "button#btn1 { text-decoration: underline;}" "button#btn1 { text-decoration-line: underline;}"

I have changed the text colour using "button#btn1 { color: #00ff00;}".

Can anyone explain why it does not work, or how to fix it?

Answer 1

For this to work, you shall have to use CSS selector for the label inside the button. Say something like button#btn1 > label {...}

A minimal example for the same:

/* button.c
 *
 * Compile: cc -ggdb button.c -o button $(pkg-config --cflags --libs gtk4)
 * Run: ./button
 *
 * Author: Mohammed Sadiq <www.sadiqpk.org>
 *
 * SPDX-License-Identifier: LGPL-2.1-or-later OR CC0-1.0
 */

#include <gtk/gtk.h>

static void
app_activated_cb (GtkApplication *app)
{
  g_autoptr(GtkCssProvider) css_provider = NULL;
  GtkWindow *window;
  GtkWidget *button;

  button = gtk_button_new_with_label ("Click me!");
  gtk_widget_set_name (button, "main");
  css_provider = gtk_css_provider_new ();
  gtk_css_provider_load_from_data (css_provider,
                                   "button#main > label { text-decoration: underline white;}", -1);
  gtk_style_context_add_provider_for_display (gdk_display_get_default (),
                                              GTK_STYLE_PROVIDER (css_provider),
                                              GTK_STYLE_PROVIDER_PRIORITY_APPLICATION);

  window = GTK_WINDOW (gtk_application_window_new (app));
  gtk_window_set_default_size (window, 600,400);
  gtk_window_set_child (window, button);

  gtk_window_present (window);
}

int
main (int   argc,
      char *argv[])
{
  g_autoptr(GtkApplication) app = gtk_application_new (NULL, 0);

  g_signal_connect (app, "activate", G_CALLBACK (app_activated_cb), NULL);

  return g_application_run (G_APPLICATION (app), argc, argv);
}