connect style.css

src/eepm-play-gui.gresource.xml

 <?xml version="1.0" encoding="UTF-8"?>
 <gresources>
   <gresource prefix="/ru/eepm/PlayGUI">
+    <file>style.css</file>
     <file preprocess="xml-stripblanks">window.ui</file>
     <file preprocess="xml-stripblanks">gtk/help-overlay.ui</file>
   </gresource>

src/main.py

@@ -23,7 +23,7 @@ import gi
 gi.require_version('Gtk', '4.0')
 gi.require_version('Adw', '1')
 
-from gi.repository import Gtk, Gio, Adw
+from gi.repository import Gtk, Gdk, Gio, Adw
 from .window import EepmPlayGuiWindow
 
 
@@ -36,6 +36,11 @@ class EepmPlayGuiApplication(Adw.Application):
         self.create_action('quit', lambda *_: self.quit(), ['<primary>q'])
         self.create_action('about', self.on_about_action)
 
+        provider = Gtk.CssProvider()
+        provider.load_from_resource("/ru/eepm/PlayGUI/style.css")
+        display = Gdk.Display.get_default()
+        Gtk.StyleContext.add_provider_for_display(display, provider, Gtk.STYLE_PROVIDER_PRIORITY_APPLICATION)
+
     def do_activate(self):
         """Called when the application is activated.
 

src/style.css

+.marked-for-install {
+    background-color: alpha(var(--accent-green), 0.6);
+    color: var(--accent-fg-color);
+}
+
+.marked-for-removal {
+    background-color: alpha(var(--destructive-bg-color), 0.6);
+    color: var(--destructive-fg-color);
+}
\ No newline at end of file