Avalonia/src/Avalonia.Themes.Default/ItemsControl.xaml

<Style xmlns="https://github.com/avaloniaui" Selector="ItemsControl">
  <Setter Property="Template">
    <ControlTemplate>
      <Border Background="{TemplateBinding Background}"
              BorderBrush="{TemplateBinding BorderBrush}"
              BorderThickness="{TemplateBinding BorderThickness}"
              Padding="{TemplateBinding Padding}">
        <ItemsPresenter Name="PART_ItemsPresenter"
                        Items="{TemplateBinding Items}"
                        ItemsPanel="{TemplateBinding ItemsPanel}"
                        ItemTemplate="{TemplateBinding ItemTemplate}"/>
      </Border>
    </ControlTemplate>
  </Setter>
</Style>