Check The GitHub Repository

Sugar Font Editor Activity

Kids Make Fonts

GTK3 and CSS


By Dave Crossland (GSoC Mentor)

Eli pointed out that GTK+3 can be styled with CSS, pointing to the example of

Sam P noted that it is CSS for GTK v3.18, and GTK CSS was overhauled in v3.20 to a new, stabilized API:

3.20 will probably not be on the XO-1 until the XO-1 kernel is updated to a recent version (if ever!)

3.20 is already here or coming to Fedora, Debian, Ubuntu, etc.

3.20 just changes the name of the elements. You can explore it by using the “CSS Nodes” view in the GTK+ inspector. It is also included in the docs for all the widgets, eg at

GtkButton has a single CSS node with name button. The node will get the style classes .image-button or .text-button, if the content is just an image or label, respectively. It may also receive the .flat style class.

Other style classes that are commonly used with GtkButton include .suggested-action and .destructive-action. In special cases, buttons can be made round by adding the .circular style class.

Button-like widgets like GtkToggleButton, GtkMenuButton, GtkVolumeButton, GtkLockButton, GtkColorButton, GtkFontButton or GtkFileChooserButton use style classes such as .toggle, .popup, .scale, .lock, .color, .font, .file to differentiate themselves from a plain GtkButton.

This GTK-CSS is like:

button {
    background: green;

button.flat {
    box-shadow: none;

Here’s a copy of for reference:

from gi.repository import Gtk, Gdk
import sys

class MyWindow(Gtk.Window):

    def __init__(self):
        Gtk.Window.__init__(self, title="Hello World")
        self.set_default_size(600, 300) = Gtk.HBox()

        self.button1 = Gtk.Button(label="Hello")
        self.button1.connect("clicked", self.on_button1_clicked), True, True, 0)

        self.button2 = Gtk.Button(label="Goodbye")
        self.button2.connect("clicked", self.on_button2_clicked), True, True, 0)

    def on_button1_clicked(self, widget):

    def on_button2_clicked(self, widget):

def main(argv):

    def gtk_style():
        css = b"""
* {
    transition-property: color, background-color, border-color, background-image, padding, border-width;
    transition-duration: 1s;
    font: Cantarell 20px;
GtkWindow {
    background: linear-gradient(153deg, #151515, #151515 5px, transparent 5px) 0 0,
                linear-gradient(333deg, #151515, #151515 5px, transparent 5px) 10px 5px,
                linear-gradient(153deg, #222, #222 5px, transparent 5px) 0 5px,
                linear-gradient(333deg, #222, #222 5px, transparent 5px) 10px 10px,
                linear-gradient(90deg, #1b1b1b, #1b1b1b 10px, transparent 10px),
                linear-gradient(#1d1d1d, #1d1d1d 25%, #1a1a1a 25%, #1a1a1a 50%, transparent 50%, transparent 75%, #242424 75%, #242424);
    background-color: #131313;
    background-size: 20px 20px;
.button {
    color: black;
    background-color: #bbb;
    border-style: solid;
    border-width: 2px 0 2px 2px;
    border-color: #333;
    padding: 12px 4px;
.button:first-child {
    border-radius: 5px 0 0 5px;
.button:last-child {
    border-radius: 0 5px 5px 0;
    border-width: 2px;
.button:hover {
    padding: 12px 48px;
    background-color: #4870bc;
.button *:hover {
    color: white;
.button:active {
    background-color: #993401;
        style_provider = Gtk.CssProvider()


    win = MyWindow()
    win.connect("delete-event", Gtk.main_quit)

if __name__ == "__main__":