c gtk3 style - button's background doesn't change - c

Question

I wrote program using GTK3 with css styling and it works perfect on my KDE.
But problem is that on ubuntu and windows 10 styling only works partially.
I have css file like this:
window {
background-color: white;
}
button {
border: none;
color: white;
padding: 15px 32px;
text-decoration: none;
font-size: 16px;
background-color: #555555;
}
Everything works except changing background of buttons.
It's how I load css:
GtkCssProvider *provider = gtk_css_provider_new ();
gtk_css_provider_load_from_path (provider, "styles.css", NULL);
gtk_style_context_add_provider_for_screen(gdk_screen_get_default(),
GTK_STYLE_PROVIDER(provider),
GTK_STYLE_PROVIDER_PRIORITY_USER);
How can I make it work?

Answer 1

I found solution:
window {
background-color: white;
}
button {
border: none;
padding: 0px;
text-decoration: none;
font-size: 16px;
}
button > label{
padding: 15px 32px;
background-color: #555555;
color: white;
}

Answer 2

You can change by writing css on ~/.config/gtk-3.0/gtk.css.
button.titlebutton.close:backdrop {
background-color: transparent;
}
button.titlebutton.close {
background-color: #theme_selected_bg_color;
}
References:
https://github.com/nana-4/materia-theme/issues/370#issuecomment-481256130
https://asukiaaa.blogspot.com/2022/07/change-color-of-close-button-of-ubuntu2204.html