// WPF — ручна підміна теми
private void SwitchTheme(string theme)
{
    var dictionaries = Application.Current.Resources.MergedDictionaries;
    dictionaries.Clear();
    
    dictionaries.Add(new ResourceDictionary 
    { 
        Source = new Uri($"Themes/{theme}.xaml", UriKind.Relative) 
    });
}

<Application xmlns="https://github.com/avaloniaui"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             x:Class="MyApp.App">
    <Application.Styles>
        <!-- Fluent Theme -->
        <FluentTheme />
    </Application.Styles>
</Application>

<Application xmlns="https://github.com/avaloniaui"
             RequestedThemeVariant="Dark">
    <Application.Styles>
        <FluentTheme />
    </Application.Styles>
</Application>

<Window xmlns="https://github.com/avaloniaui"
        RequestedThemeVariant="Light">
    <!-- Контент -->
</Window>

<Border RequestedThemeVariant="Dark">
    <!-- Темний контент всередині світлого вікна -->
</Border>

using Avalonia;
using Avalonia.Styling;

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }
    
    private void SwitchToDark()
    {
        // Змінити тему на рівні Application
        Application.Current.RequestedThemeVariant = ThemeVariant.Dark;
    }
    
    private void SwitchToLight()
    {
        Application.Current.RequestedThemeVariant = ThemeVariant.Light;
    }
    
    private void FollowSystem()
    {
        Application.Current.RequestedThemeVariant = ThemeVariant.Default;
    }
}

public partial class SettingsViewModel : ObservableObject
{
    [ObservableProperty]
    private string _selectedTheme = "Default";
    
    partial void OnSelectedThemeChanged(string value)
    {
        var themeVariant = value switch
        {
            "Light" => ThemeVariant.Light,
            "Dark" => ThemeVariant.Dark,
            _ => ThemeVariant.Default
        };
        
        Application.Current.RequestedThemeVariant = themeVariant;
    }
}

<StackPanel Margin="20">
    <TextBlock Text="Тема:" FontWeight="Bold"/>
    <ComboBox SelectedItem="{Binding SelectedTheme}" Margin="0,5,0,0">
        <ComboBoxItem Content="Системна (Default)"/>
        <ComboBoxItem Content="Світла (Light)"/>
        <ComboBoxItem Content="Темна (Dark)"/>
    </ComboBox>
</StackPanel>

<Application RequestedThemeVariant="Default">
    <Application.Styles>
        <FluentTheme />
    </Application.Styles>
</Application>

<Border Background="{DynamicResource SystemAccentColor}"
        BorderBrush="{DynamicResource SystemControlForegroundBaseMediumBrush}"
        BorderThickness="1"
        CornerRadius="8"
        Padding="20">
    <TextBlock Text="Акцентний колір"
               Foreground="{DynamicResource SystemControlForegroundBaseHighBrush}"/>
</Border>

<Application.Resources>
    <ResourceDictionary>
        <ResourceDictionary.ThemeDictionaries>
            <!-- Світла тема -->
            <ResourceDictionary x:Key="Light">
                <SolidColorBrush x:Key="MyCustomBrush" Color="#2196F3"/>
                <x:Double x:Key="MyCustomOpacity">0.9</x:Double>
            </ResourceDictionary>
            
            <!-- Темна тема -->
            <ResourceDictionary x:Key="Dark">
                <SolidColorBrush x:Key="MyCustomBrush" Color="#64B5F6"/>
                <x:Double x:Key="MyCustomOpacity">0.8</x:Double>
            </ResourceDictionary>
        </ResourceDictionary.ThemeDictionaries>
    </ResourceDictionary>
</Application.Resources>

<Border Background="{DynamicResource MyCustomBrush}"
        Opacity="{DynamicResource MyCustomOpacity}">
    <!-- Автоматично змінюється при зміні теми -->
</Border>

<Application xmlns="https://github.com/avaloniaui">
    <Application.Styles>
        <SimpleTheme />
    </Application.Styles>
</Application>

dotnet add package Material.Avalonia

<Application xmlns="https://github.com/avaloniaui"
             xmlns:themes="clr-namespace:Material.Styles.Themes;assembly=Material.Styles">
    <Application.Styles>
        <themes:MaterialTheme BaseTheme="Dark" PrimaryColor="Blue" SecondaryColor="Lime"/>
    </Application.Styles>
</Application>

dotnet add package Semi.Avalonia

<Application xmlns="https://github.com/avaloniaui"
             xmlns:semiTheme="clr-namespace:Semi.Avalonia.Themes;assembly=Semi.Avalonia">
    <Application.Styles>
        <semiTheme:SemiTheme Locale="zh-CN"/>
    </Application.Styles>
</Application>

<Application xmlns="https://github.com/avaloniaui">
    <Application.Styles>
        <FluentTheme>
            <FluentTheme.Palettes>
                <ColorPaletteResources x:Key="Light" Accent="#FF6B35" AltHigh="White"/>
                <ColorPaletteResources x:Key="Dark" Accent="#FF6B35" AltHigh="Black"/>
            </FluentTheme.Palettes>
        </FluentTheme>
    </Application.Styles>
</Application>

var fluentTheme = Application.Current.Styles.OfType<FluentTheme>().FirstOrDefault();
if (fluentTheme != null)
{
    fluentTheme.Palettes[ThemeVariant.Light].Accent = Color.Parse("#FF6B35");
    fluentTheme.Palettes[ThemeVariant.Dark].Accent = Color.Parse("#FF6B35");
}

<FluentTheme DensityStyle="Compact"/>
<!-- або -->
<FluentTheme DensityStyle="Normal"/>

Themes/
├── Light.xaml
├── Dark.xaml
└── Blue.xaml

<Application.Resources>
    <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary Source="Themes/Light.xaml"/>
        </ResourceDictionary.MergedDictionaries>
    </ResourceDictionary>
</Application.Resources>

private void SwitchTheme(string theme)
{
    var dictionaries = Application.Current.Resources.MergedDictionaries;
    dictionaries.Clear();
    dictionaries.Add(new ResourceDictionary 
    { 
        Source = new Uri($"Themes/{theme}.xaml", UriKind.Relative) 
    });
}

<Application RequestedThemeVariant="Default">
    <Application.Styles>
        <FluentTheme />
    </Application.Styles>
</Application>

Application.Current.RequestedThemeVariant = ThemeVariant.Dark;

<Window xmlns="https://github.com/avaloniaui"
        x:Class="MyApp.MainWindow"
        Title="Theme Switcher" Width="400" Height="300">
    
    <StackPanel Margin="20" Spacing="10">
        <ToggleSwitch Content="Темна тема" 
                      IsChecked="{Binding IsDarkTheme}"
                      OffContent="Світла тема"
                      OnContent="Темна тема"/>
        
        <Border Background="{DynamicResource SystemAccentColor}"
                Padding="20"
                CornerRadius="8">
            <TextBlock Text="Акцентний колір"
                       Foreground="White"
                       FontSize="16"/>
        </Border>
        
        <Button Content="Кнопка з темою" HorizontalAlignment="Stretch"/>
        
        <TextBox Watermark="Введіть текст..."/>
    </StackPanel>
</Window>

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
        DataContext = new MainViewModel();
    }
}

public partial class MainViewModel : ObservableObject
{
    [ObservableProperty]
    private bool _isDarkTheme;
    
    partial void OnIsDarkThemeChanged(bool value)
    {
        Application.Current.RequestedThemeVariant = value 
            ? ThemeVariant.Dark 
            : ThemeVariant.Light;
    }
}

public partial class MainViewModel : ObservableObject
{
    [ObservableProperty]
    private string _selectedColor = "Blue";
    
    partial void OnSelectedColorChanged(string value)
    {
        var color = value switch
        {
            "Red" => Color.Parse("#F44336"),
            "Green" => Color.Parse("#4CAF50"),
            "Purple" => Color.Parse("#9C27B0"),
            "Orange" => Color.Parse("#FF9800"),
            _ => Color.Parse("#2196F3") // Blue
        };
        
        var fluentTheme = Application.Current.Styles.OfType<FluentTheme>().FirstOrDefault();
        if (fluentTheme != null)
        {
            fluentTheme.Palettes[ThemeVariant.Light].Accent = color;
            fluentTheme.Palettes[ThemeVariant.Dark].Accent = color;
        }
    }
}

public partial class SettingsViewModel : ObservableObject
{
    [ObservableProperty]
    private string _themeMode = "System";
    
    [ObservableProperty]
    private string _currentActiveTheme;
    
    public SettingsViewModel()
    {
        // Завантажити збережені налаштування
        LoadSettings();
        
        // Підписатися на зміни теми
        Application.Current.ActualThemeVariantChanged += OnThemeChanged;
        
        UpdateCurrentTheme();
    }
    
    partial void OnThemeModeChanged(string value)
    {
        var themeVariant = value switch
        {
            "Light" => ThemeVariant.Light,
            "Dark" => ThemeVariant.Dark,
            _ => ThemeVariant.Default
        };
        
        Application.Current.RequestedThemeVariant = themeVariant;
        SaveSettings();
    }
    
    private void OnThemeChanged(object sender, EventArgs e)
    {
        UpdateCurrentTheme();
    }
    
    private void UpdateCurrentTheme()
    {
        CurrentActiveTheme = Application.Current.ActualThemeVariant == ThemeVariant.Dark 
            ? "Темна" 
            : "Світла";
    }
    
    private void LoadSettings()
    {
        // Завантажити з файлу або реєстру
        ThemeMode = Preferences.Get("ThemeMode", "System");
    }
    
    private void SaveSettings()
    {
        // Зберегти у файл або реєстр
        Preferences.Set("ThemeMode", ThemeMode);
    }
}