WPF Listbox Show Button in ItemTemplate on MouseOver

Ok, try this in your button declaration:

<Button x:Name="sideButton" Width="20">
    <Button.Style>
        <Style TargetType="{x:Type Button}">
            <Setter Property="Visibility" Value="Hidden" />
            <Style.Triggers>
                <DataTrigger Binding="{Binding RelativeSource={RelativeSource Mode=FindAncestor,AncestorType={x:Type ListBoxItem}},Path=IsMouseOver}" Value="True">
                    <Setter Property="Visibility" Value="Visible" />
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </Button.Style>
</Button>

So I’m using a style with a trigger to look back up the visual tree until I find a ListBoxItem, and when its IsMouseOver property flips over to True I set the button‘s visibility to Visible.

See if it’s close to what you want.