<Style TargetType="Label">
    <Setter Property="BackgroundColor" Value="Transparent" />
    //Something like below?
    <Setter Property="AbsoluteLayout.LayoutFlags" Value="PositionProportional | SizeProportional" />
</Style>

....

<Label Text="0" AbsoluteLayout.LayoutBounds="0.5, 0.00499999999999998, AutoSize, AutoSize"/>