Toolkit2/Toolkit.UI.Controls.Avalonia/ContentBadge/ContentBadge.axaml

<ResourceDictionary
    xmlns="https://github.com/avaloniaui"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:controls="using:Toolkit.UI.Controls.Avalonia">
    <ControlTheme x:Key="{x:Type controls:ContentBadge}" TargetType="controls:ContentBadge">
        <Setter Property="Template">
            <ControlTemplate>
                <Grid>
                    <ContentPresenter Content="{TemplateBinding Content}" ContentTemplate="{TemplateBinding ContentTemplate}" />
                    <ContentControl x:Name="BadgeContent" />
                </Grid>
            </ControlTemplate>
        </Setter>
    </ControlTheme>
</ResourceDictionary>