Avalonia/samples/XamlTestApplicationPcl/TabControl.paml

<Style xmlns="https://github.com/perspex" Selector="TabControl">
  <Setter Property="Template">
    <ControlTemplate>
      <Grid RowDefinitions="Auto,*">
        <TabStrip Items="{TemplateBinding Items}"
                  SelectedIndex="{TemplateBinding Path=SelectedIndex, Mode=TwoWay}"/>
        <Carousel Items="{TemplateBinding Items}"
                  MemberSelector="Content"
                  SelectedIndex="{TemplateBinding Path=SelectedIndex}"
                  Transition="{TemplateBinding Transition}"
                  Grid.Row="1"/>
      </Grid>
    </ControlTemplate>
  </Setter>
</Style>