Add theme switcher code snippets and supporting styles

Author: dvoituron

examples/Demo/FluentUI.Demo.Client/Documentation/Components/Theme/Dark/Examples/ThemeSnippet.razor

@@ -0,0 +1,40 @@
+@inject IJSRuntime JSRuntime
+
+<FluentStack Style="background-color: var(--colorBrandBackgroundHover);"
+             HorizontalGap="24px"
+             HorizontalAlignment="HorizontalAlignment.Right">
+
+    @* ************************ *@
+    @* Option 1: Sun/Moon icons *@
+    @* ************************ *@
+    <FluentButton Appearance="ButtonAppearance.Transparent"
+                  IconOnly="true"
+                  Class="fluent-header-hover"
+                  Title="Switch to Light/Dark theme"
+                  OnClick="@(async e => await JSRuntime.InvokeVoidAsync("Blazor.theme.switchTheme"))">
+        @* Dark icon *@
+        <FluentIcon Class="hidden-if-light"
+                    Value="@(new Icons.Filled.Size20.WeatherSunny().WithColor(SystemColors.Neutral.ForegroundOnBrand))" />
+        @* Light icon *@
+        <FluentIcon Class="hidden-if-dark"
+                    Value="@(new Icons.Filled.Size20.WeatherMoon().WithColor(SystemColors.Neutral.ForegroundOnBrand))" />
+    </FluentButton>
+
+    @* ************************* *@
+    @* Option 2: Dark theme icon *@
+    @* ************************* *@
+    <FluentButton Appearance="ButtonAppearance.Transparent"
+                  IconOnly="true"
+                  Class="fluent-header-hover"
+                  Title="Switch to Light/Dark theme"
+                  OnClick="@(async e => await JSRuntime.InvokeVoidAsync("Blazor.theme.switchTheme"))">
+        @* Dark icon *@
+        <FluentIcon Class="hidden-if-light"
+                    Value="@(new Icons.Filled.Size20.DarkTheme().WithColor(SystemColors.Neutral.ForegroundOnBrand))" />
+        @* Light icon *@
+        <FluentIcon Class="hidden-if-dark"
+                    Style="transform: rotate(180deg);"
+                    Value="@(new Icons.Filled.Size20.DarkTheme().WithColor(SystemColors.Neutral.ForegroundOnBrand))" />
+    </FluentButton>
+
+</FluentStack>

examples/Demo/FluentUI.Demo.Client/Documentation/Components/Theme/Dark/ThemeDark.md

@@ -11,6 +11,8 @@ This theme is designed to provide a visually appealing and comfortable user expe
 You can easily switch between light and dark themes using the provided JavaScript functions: 
 `Blazor.theme.setDarkTheme` and `Blazor.theme.setLightTheme`.
 
+> [!TIP] See to the section **Code snippets** at the bottom of this page for ready-to-use code examples.
+
 ## Example
 
 ```csharp
@@ -91,3 +93,23 @@ Or to automatically switch themes based on system preferences.
     });
 </script>
 ```
+
+## Code snippets
+
+In this example, two buttons are created that allows users to switch between light and dark themes.
+
+1. The first/left example uses two icons:
+    - A **dark icon** (a sun) that is only visible when the light theme is active.
+      The internal CSS class `hidden-if-light` is used to hide the icon when the light theme is active.
+    - A **light icon** (a moon) that is only visible when the dark theme is active.
+      The internal CSS class `hidden-if-dark` is used to hide the icon when the dark theme is active.
+
+2. The second/right example uses the same **DarkTheme icon** but changes its appearance based on the current theme: `Style="transform: rotate(180deg);"`
+
+In these two examples, when the button is **hovered**, the icon color changes to indicate interactivity, using the class `fluent-header-hover`.
+
+When the user clicks the button, the `OnClick` event handler calls the JavaScript function `Blazor.theme.switchTheme` to toggle between light and dark themes.
+(note the use of `@inject IJSRuntime JSRuntime` to invoke JavaScript functions from Blazor).
+The `body data-theme` attribute is automatically updated, and the `themeChanged` event is triggered.
+
+{{ ThemeSnippet }}

src/Core/Components/Layout/FluentLayoutItem.razor.css

@@ -73,3 +73,8 @@
 .fluent-layout[mobile] .fluent-layout-item[area="footer"] {
   line-height: var(--lineHeightBase100);
 }
+
+/* For external use */
+.fluent-header-hover:hover {
+  background-color: var(--colorBrandBackground);
+}

src/Core/Components/Theme/Styles/ThemeStyles.css

@@ -0,0 +1,9 @@
+body[data-theme="light"] .hidden-if-light,
+body:not([data-theme]) .hidden-if-light,
+body[data-theme=""] .hidden-if-light {
+  display: none;
+}
+
+body[data-theme="dark"] .hidden-if-dark {
+  display: none;
+}