Add demo toolbar with custom background to showcase overflow button fix

Adds a second toolbar example in both MainDemo and MaterialDesign3.Demo
that uses a custom background with overflow items forced via
OverflowMode=Always, demonstrating that the overflow button now
inherits the toolbar's background color.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Keboo

src/MainDemo.Wpf/MenusAndToolBars.xaml

@@ -378,6 +378,22 @@
       </ToolBarTray>
     </smtx:XamlDisplay>
 
+    <smtx:XamlDisplay Margin="0,16,0,16" UniqueKey="menus_toolbar_custom_bg">
+      <ToolBarTray>
+        <ToolBar Background="{DynamicResource MaterialDesign.Brush.Primary.Dark}"
+                 ClipToBounds="False"
+                 Style="{StaticResource MaterialDesignToolBar}">
+          <Button Content="{materialDesign:PackIcon Kind=ContentSave}" ToolTip="Save" />
+          <Button Content="{materialDesign:PackIcon Kind=ContentCut}" ToolTip="Cut" />
+          <Button Content="{materialDesign:PackIcon Kind=ContentCopy}" ToolTip="Copy" />
+          <Button Content="{materialDesign:PackIcon Kind=ContentPaste}" ToolTip="Paste" />
+          <Button Content="{materialDesign:PackIcon Kind=FormatBold}" ToolBar.OverflowMode="Always" />
+          <Button Content="{materialDesign:PackIcon Kind=FormatItalic}" ToolBar.OverflowMode="Always" />
+          <Button Content="{materialDesign:PackIcon Kind=FormatUnderline}" ToolBar.OverflowMode="Always" />
+        </ToolBar>
+      </ToolBarTray>
+    </smtx:XamlDisplay>
+
     <Rectangle Style="{StaticResource PageSectionSeparator}" />
     <TextBlock Style="{StaticResource PageSectionTitleTextBlock}" Text="Context Menus" />
 

src/MaterialDesign3.Demo.Wpf/MenusAndToolBars.xaml

@@ -346,6 +346,24 @@
       </ToolBarTray>
     </smtx:XamlDisplay>
 
+    <smtx:XamlDisplay Margin="5,16,0,16"
+                      DockPanel.Dock="Top"
+                      UniqueKey="menus_toolbar_custom_bg">
+      <ToolBarTray>
+        <ToolBar Background="{DynamicResource MaterialDesign.Brush.Primary.Dark}"
+                 ClipToBounds="False"
+                 Style="{StaticResource MaterialDesignToolBar}">
+          <Button Content="{materialDesign:PackIcon Kind=ContentSave}" ToolTip="Save" />
+          <Button Content="{materialDesign:PackIcon Kind=ContentCut}" ToolTip="Cut" />
+          <Button Content="{materialDesign:PackIcon Kind=ContentCopy}" ToolTip="Copy" />
+          <Button Content="{materialDesign:PackIcon Kind=ContentPaste}" ToolTip="Paste" />
+          <Button Content="{materialDesign:PackIcon Kind=FormatBold}" ToolBar.OverflowMode="Always" />
+          <Button Content="{materialDesign:PackIcon Kind=FormatItalic}" ToolBar.OverflowMode="Always" />
+          <Button Content="{materialDesign:PackIcon Kind=FormatUnderline}" ToolBar.OverflowMode="Always" />
+        </ToolBar>
+      </ToolBarTray>
+    </smtx:XamlDisplay>
+
     <Rectangle Style="{StaticResource PageSectionSeparator}" />
     <TextBlock Style="{StaticResource PageSectionTitleTextBlock}" Text="Context Menus" />