<Grid>
  <Grid.Resources>
    <Style x:Key="ListBoxTemplate" TargetType="ListBox">
      <Setter Property="Template">
        <Setter.Value>
          <ControlTemplate TargetType="ListBox">
            <Grid>
              <Ellipse Stroke="{TemplateBinding BorderBrush}"
                  StrokeThickness="{TemplateBinding BorderThickness}"
                  Fill="{TemplateBinding Background}"/>
              <ScrollViewer HorizontalScrollBarVisibility="Auto"
                          VerticalScrollBarVisibility="Auto">
                <ItemsPresenter HorizontalAlignment="Center"
                              VerticalAlignment="Center"/>
              </ScrollViewer>
            </Grid>
          </ControlTemplate>
        </Setter.Value>
      </Setter>
    </Style>

    <src:Items x:Key="myItems"/>
  </Grid.Resources>

  <ListBox ItemsSource="{StaticResource myItems}" 
         Style="{StaticResource ListBoxTemplate}"
         Width="250" Height="250" 
         Background="Aquamarine" BorderBrush="Navy" BorderThickness="5"/>
</Grid>

Public Class Items
    Inherits System.Collections.ObjectModel.ObservableCollection(Of String)

    Public Sub New()
        Add("Item 1")
        Add("Item 2")
        Add("Item 3")
        Add("Item 4")
        Add("Item 5")
    End Sub
End Class

public class Items : 
    System.Collections.ObjectModel.ObservableCollection<string>
{
    public Items()
    {
        Add("Item 1");
        Add("Item 2");
        Add("Item 3");
        Add("Item 4");
        Add("Item 5");
    }
}