<Window x:Class="MyApp.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:syncfusionskin="clr-namespace:Syncfusion.SfSkinManager;assembly=Syncfusion.SfSkinManager.WPF"
        syncfusionskin:SfSkinManager.Theme="{syncfusionskin:SkinManagerExtension ThemeName=Windows11Light}">
    <Grid>
        <!-- Your controls here - theme automatically applied -->
    </Grid>
</Window>

using Syncfusion.SfSkinManager;

public partial class MainWindow : Window
{
    public MainWindow()
    {
        // Enable theme as default style
        SfSkinManager.ApplyThemeAsDefaultStyle = true;
        
        // Apply theme to this window and all child controls
        SfSkinManager.SetTheme(this, new Theme("Windows11Light"));
        
        InitializeComponent();
    }
}

public partial class App : Application
{
    protected override void OnStartup(StartupEventArgs e)
    {
        SfSkinManager.ApplyThemeAsDefaultStyle = true;
        SfSkinManager.ApplicationTheme = new Theme("Fluent
Dark");
        
        base.OnStartup(e);
    }
}

// Example: Switch theme when user selects from dropdown
private void OnThemeSelectionChanged(string themeName)
{
    SfSkinManager.SetTheme(this, new Theme(themeName));
}

string customThemeName = "MyCustomTheme";
string baseThemeName = "Windows11Light";

// Register custom theme (assuming custom theme assembly is referenced)
SkinHelper customThemeInstance = new MyCustomThemeSkinHelper();
SfSkinManager.RegisterTheme(customThemeName, customThemeInstance);

// Apply the custom theme
SfSkinManager.SetTheme(this, new Theme($"{customThemeName};{baseThemeName}"));

// Example: Customize Windows 11 Light theme colors
var themeSettings = new Windows11LightThemeSettings();
themeSettings.Palette = new Windows11Palette 
{ 
    PrimaryColor = Colors.Blue,
    SecondaryColor = Colors.LightBlue
};

SfSkinManager.RegisterThemeSettings("Windows11Light", themeSettings);
SfSkinManager.SetTheme(this, new Theme("Windows11Light"));