docs: use theme service

doc/Learn/ThemeService/HowTo-UseThemeService.md

@@ -0,0 +1,49 @@
+---
+uid: Uno.Extensions.ThemeService.Overview
+---
+
+# How to use Theme Service
+
+This topic explains how to use the `ThemeService` for runtime theme switching and persisting user theme preferences.
+
+## Step-by-steps
+
+1. **Register ThemeService**:
+    Add the `ThemeService` to your project's host builder configuration.
+
+    ```csharp
+    public partial class App : Application
+    {
+        protected override void OnLaunched(LaunchActivatedEventArgs args)
+        {
+            var builder = this.CreateBuilder(args)
+                .Configure(host => host
+                    .UseThemeSwitching()
+                );
+        }
+    }
+    ```
+
+2. **Consume ThemeService**:
+    Inject the ThemeService into your view models or other services where you need to manipulate the theme.
+
+    ```csharp
+    public class SettingsViewModel
+    {
+        private readonly IThemeService _themeService;
+        public SettingsViewModel(IThemeService themeService)
+        {
+            _themeService = themeService;
+        }
+        public async Task ToggleThemeAsync()
+        {
+            var currentTheme = _themeService.Theme;
+            var newTheme = currentTheme == AppTheme.Dark ? AppTheme.Light : AppTheme.Dark;
+            await _themeService.SetThemeAsync(newTheme);
+        }
+    }
+    ```
+
+## Source Code
+
+[ThemeService Implementation](https://github.com/unoplatform/uno.extensions/blob/51c9c1ef14f686363f946588733faecc5a1863ff/src/Uno.Extensions.Core.UI/Toolkit/ThemeService.cs)

doc/Learn/ThemeService/toc.yml

@@ -0,0 +1,2 @@
+- name: Theme Service
+  href: xref:Uno.Extensions.ThemeService.Overview

doc/toc.yml

@@ -47,6 +47,9 @@
 - name: .NET MAUI Embedding
   href: Learn/Maui/toc.yml
   topicHref: xref:Uno.Extensions.Maui.Overview
+- name: Theme Service
+  href: Learn/ThemeService/toc.yml
+  topicHref: xref:Uno.Extensions.ThemeService.Overview
 - name: Reference
   items:
     - name: MVUX