XAML-Map-Control/SampleApps/AvaloniaApp/App.axaml

<Application xmlns="https://github.com/avaloniaui"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             x:Class="AvaloniaApp.App"
             RequestedThemeVariant="Default">
    <Application.Styles>
        <FluentTheme />
        <StyleInclude Source="avares://MapControl.Avalonia/Themes/Generic.axaml"/>
    </Application.Styles>
</Application>