fix: fix highlighting in single-instance plugin (tauri-apps#2786)

src/content/docs/plugin/single-instance.mdx

@@ -95,31 +95,22 @@ So, the closure should look like below
 
 By default, when you initiate a new instance while the application is already running, no action is taken. To focus the window of the running instance when user tries to open a new instance, alter the callback closure as follows:
 
-```rust title="src-tauri/src/lib.rs" {1} {5-7} {12-21}
+```rust title="src-tauri/src/lib.rs" {1} {5-12}
 use tauri::{AppHandle, Manager};
 
 pub fn run() {
     let mut builder = tauri::Builder::default();
     #[cfg(desktop)]
     {
         builder = builder.plugin(tauri_plugin_single_instance::init(|app, args, cwd| {
-            let _ = show_window(app);
+            let _ = app.get_webview_window("main")
+                       .expect("no main window")
+                       .set_focus();
         }));
     }
 
     builder
         .run(tauri::generate_context!())
         .expect("error while running tauri application");
 }
-
-fn show_window(app: &AppHandle) {
-    let windows = app.webview_windows();
-
-    windows
-        .values()
-        .next()
-        .expect("Sorry, no window found")
-        .set_focus()
-        .expect("Can't Bring Window to Focus");
-}
 ```