CSS opacity not respected for window

[MarcusBoay]

CSS opacity doesn't seem to be respected for window. There is no opacity and the red seems to be a dull color. For some strange reason, this issue disappears when I set window.set_opacity(0.99).

source code

use gtk::{
    gdk::Display,
    prelude::*,
    CssProvider,
};

fn main() {
    let app = gtk::Application::builder()
        .application_id("rlogout")
        .build();
    app.connect_startup(|_| load_css());
    app.connect_activate(build_ui);
    app.run();
}

fn build_ui(app: &gtk::Application) {
    let window = gtk::ApplicationWindow::builder()
        .application(app)
        .build();
    window.set_fullscreened(true);
    // window.set_opacity(0.99);
    window.present();
}

fn load_css() {
    let provider = CssProvider::new();
    provider.load_from_string("window { opacity: 0.2; background-color: red; }");

    gtk::style_context_add_provider_for_display(
        &Display::default().expect("Could not connect to a display."),
        &provider,
        gtk::STYLE_PROVIDER_PRIORITY_APPLICATION,
    );
}

Cargo.toml:

...

[dependencies.gtk]
package = "gtk4"
version = "0.8.2"
features = ["v4_14"]

According to the Hyprland dev, this is relevant in the logs with WAYLAND_DEBUG=1: hyprwm/Hyprland#6692 (comment)

[MarcusBoay]

Ok, it looks like it is working as expected under the xdg protocol. I needed gtk4-layer-shell.