Avalonia/samples/XamlTestApplicationPcl/TabStrip.paml

<Styles xmlns="https://github.com/perspex">
  <Style Selector="TabStrip">
    <Setter Property="Template">
      <ControlTemplate>
        <ItemsPresenter Items="{TemplateBinding Items}"
                        ItemsPanel="{TemplateBinding ItemsPanel}"/>
      </ControlTemplate>
    </Setter>
  </Style>
  <Style Selector="TabStrip /template/ StackPanel">
    <Setter Property="Gap" Value="16"/>
    <Setter Property="Orientation" Value="Horizontal"/>
  </Style>
</Styles>