I have a little problem setting up the player in my platform (XAML WINRT, Windows Phone 8.1 application), I'm trying to remove the circle around the Play / Pause and Full Screen buttons:

I would like them to look like this:

I have access to the default XAML of the Play / Pause button:
However, Blend does not allow me to create a copy of the element so that I can customize it:

Do you know what I can do to fix this? Or is there another solution to remove the circle around the play / pause?
Edit:
To get the second image, click the Photoshop button to show what I would like to have.
, "TransportBarButtonStyle" AppBarButton, Blend Visual Studio .
codeplex :
https://playerframework.codeplex.com/SourceControl/latest#Universal.Xaml.Core/Themes/Classic.xaml, :
<Style x:Key="TransportBarButtonStyle" TargetType="AppBarButton">