Avalonia/samples/VirtualizationDemo/App.xaml

<Application
    xmlns="https://github.com/avaloniaui" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    x:Class="VirtualizationDemo.App">
    <Application.Styles>
        <StyleInclude Source="avares://Avalonia.Themes.Default/DefaultTheme.xaml"/>
        <StyleInclude Source="avares://Avalonia.Themes.Default/Accents/BaseLight.xaml"/>
    </Application.Styles>
</Application>