CSS styles are not being applied on a Gtk widget

Question

Another user here on StackOverflow has some problems styling his Gtk application with CSS. I found a solution for part of the problems, but for one I don't know anything. The original post is with C code, but the following Python Minimal Reproducible Example has the same problem:

#!/usr/bin/python3
#-*-coding: utf-8-*-

import gi
gi.require_version("Gtk", "3.0")
from gi.repository import Gtk

win = Gtk.Window()
win.connect("destroy", lambda _: Gtk.main_quit())
box = Gtk.VBox()
win.add(box)
button = Gtk.Button("Button")
prov = Gtk.CssProvider.new()
prov.load_from_data("""
button {
    color: red;
    background-color: green;
    margin: 30px;
}
""".encode())
ctx = win.get_style_context()
ctx.add_provider(prov, 1000)
box.add(button)
win.show_all()
Gtk.main()

The problem is, the margins are not showing, nor the font and background color, whereas they are correctly shown in this example:

#!/usr/bin/python3
#-*-coding: utf-8-*-

import gi
gi.require_version("Gtk", "3.0")
from gi.repository import Gtk

win = Gtk.Window()
win.connect("destroy", lambda _: Gtk.main_quit())
box = Gtk.VBox()
win.add(box)
button = Gtk.Button("Button")
prov = Gtk.CssProvider.new()
prov.load_from_data("""
* {
    color: red;
    background-color: green;
    margin: 30px;
}
""".encode())
ctx = button.get_style_context()
ctx.add_provider(prov, 1000)
box.add(button)
win.show_all()
Gtk.main()

This led me to the conclusion that the selector button somehow does not do what I want and expect. Why is the selector wrong, and which would be the right selector to select the button ?

From docs: #define GTK_STYLE_PROVIDER_PRIORITY_USER 800 You should not use priorities higher than this, to give the user the last word. Maybe your GTK theme overrides your style? Have you tried it with adwaita? — Alexander Dmitriev
– Alexander Dmitriev, Commented Mar 26, 2021 at 14:32
@AlexanderDmitriev no, I tested the provided example on my machine with a priority of 1000, and it still didn't help. The problem here is a wrong selector, only I have no idea what would be the right, working selector ... — TheEagle
– TheEagle, Commented Mar 26, 2021 at 15:50

Erman Kadir Kahraman · Accepted Answer · 2023-09-04 02:47:48Z

1

Note what the documentation for gtk_style_context_add_provider() says:

Note that a style provider added by this function only affects the style of the widget to which context belongs. If you want to affect the style of all widgets, use gtk_style_context_add_provider_for_screen().

The styles apply to that widget only, not the widget and its children. The preferred way to style GTK applications is to create one stylesheet for the whole application, then use gtk_style_context_add_class to add style classes to individual widgets.

edited Sep 4, 2023 at 2:47

Erman Kadir Kahraman

7651 gold badge7 silver badges9 bronze badges

answered Mar 26, 2021 at 17:20

James Westman

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