How to make MonoGame's background transparent?

Question

I have a UWP App and I use SwapChainPanel to insert MonoGame. in Render():

_game.GraphicsDevice.Clear(Color.Transparent);

But it didn't work.

<Grid Background="White">
    <SwapChainPanel x:Name="swapChainPanel">
    </SwapChainPanel>
</Grid>

Could you help me to figure out it?
Problem picture