隔久点不用老是会忘，留个笔记。。

Python+PYGObject/PYGtk，加载 CSS 样式的演示代码

demo 运行的效果截图：

#!/usr/bin/env python3
import sys
import gi

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


class MyApplication(Gtk.Application):
	def __init__(self):
		super().__init__(application_id="com.example.MyGtkApplication")
		GLib.set_application_name('My Gtk Application')

	def do_activate(self):
		window = Gtk.ApplicationWindow(application=self, title="Hello World")
		window.present()
		button = Gtk.Button(label="Python+PyGObject+CSS修改背景色")
		button.set_name("bricks-button")
		button.set_halign(Gtk.Align.CENTER)
		button.set_valign(Gtk.Align.CENTER)
		button.set_size_request(250, 84)
		window.add(button)
		window.show_all()

		strcss="""
			#bricks-button {
				color: #F55;
				background-color: #eef;
				background-image: -gtk-scaled(url('resource://css/brick.png'), url('resource://css/brick2.png'));
				background-repeat: no-repeat;
				background-position: center;
				/* 测试 */
			}
		"""
		
		strpath="./play.css"
		fp = open(strpath, 'w')
		fp.write(strcss)
		fp.close()

		provider = Gtk.CssProvider()
		provider.connect("parsing-error", self.show_css_parsing_error)
		# fname = Gio.file_new_for_path('play.css')
		# provider.load_from_file(fname)
		# https://docs.gtk.org/gtk4/method.CssProvider.load_from_file.html
		# load_from_path, load_from_file, load_from_string
		provider.load_from_path(strpath)
		self.apply_css(window, provider)

	def show_css_parsing_error(self, provider, section, error):
		print(error.message)

	def apply_css(self, widget, provider):
		Gtk.StyleContext.add_provider(widget.get_style_context(), provider, Gtk.STYLE_PROVIDER_PRIORITY_APPLICATION)

		if isinstance(widget, Gtk.Container):
			widget.forall(self.apply_css, provider)


app = MyApplication()
exit_status = app.run(sys.argv)
sys.exit(exit_status)

官方文档：CssProvider — GNOME Python API

Deprecated since version 4.12: Use load_from_string or load_from_bytes instead

Styling GTK3 in Python with CSS (Shallow Thoughts)

控件对应的CSS选择器名称（Built-in Class Names）

css = 'button { background-color: #f00; }'

CSS选择器名称可以改（User-set Class Names）

    button_context = button.get_style_context()
    button_context.add_class("whitebutton")

控件名称，映射为 HTML 标签的ID，在CSS中使用井号选择器
（Widget Names, like CSS ID）

    label = gtk.Label()
    label.set_use_markup(True)
    label.set_line_wrap(True)
    label.set_name("red_label")
    mainbox.pack_start(label, False, False, 0)
    css = '#red_label { background-color: #f00; }'

dflabel = gtk.Label()