fix(linux): make menubar background transparent (rust-windowing#389)

* fix(linux): make menubar background transparent

* fix build

* use css provider

* remove shadow

* add changefile

* only when window is transparent

* update change file

* fix typo in changefile

Co-authored-by: Fabian-Lars <fabianlars@fabianlars.de>

.changes/linux-transparent-menubar.md

@@ -0,0 +1,5 @@
+---
+"tao": patch
+---
+
+Change menubar background color to transparent on Linux when the window is transparent.

src/platform_impl/linux/window.rs

@@ -193,6 +193,19 @@ impl Window {
     window.add(&window_box);
 
     let mut menu_bar = gtk::MenuBar::new();
+
+    if attributes.transparent {
+      let style_context = menu_bar.style_context();
+      let css_provider = gtk::CssProvider::new();
+      let theme = r#"
+          menubar {
+            background-color: transparent;
+            box-shadow: none;
+          }
+        "#;
+      css_provider.load_from_data(theme.as_bytes());
+      style_context.add_provider(&css_provider, 600);
+    }
     window_box.pack_start(&menu_bar, false, false, 0);
     if let Some(window_menu) = attributes.window_menu {
       window_menu.generate_menu(&mut menu_bar, &window_requests_tx, &accel_group, window_id);