WPF更改网格和网格边框不透明度而不影响子项

I have a grid that i want to make opacity 0.5. i also have a border for this grid in order to make it rounded cornered and i want this border to also have opacity 0.5. i want all this without effecting the content of the grid. i succeeded changing the opacity of the Grid without effecting the content:I have a grid that i want to make opacity 0.5.