使用支持库中的 BottomSheet 时如何调暗背景？

怎样才能让背景像显示的那样变暗here https://material-design.storage.googleapis.com/publish/material_v_8/material_ext_publish/0Bzhp5Z4wHba3UzA3RDctV2k0YUk/components_bottomsheets_modal2.png?

我已经使用正常设置CoordinatorLayout和BottomSheetBehavior.

这将仅显示底部工作表。

public class MyBottomSheet extends BottomSheetDialogFragment {
    private static final String TAG = "MyBottomSheet";

    @NonNull
    @Override
    public Dialog onCreateDialog(final Bundle savedInstanceState) {
        final BottomSheetDialog dialog = (BottomSheetDialog) super.onCreateDialog(savedInstanceState);

        final View view = View.inflate(getContext(), R.layout.my_custom_view, null);

        dialog.setContentView(view);
        behavior = BottomSheetBehavior.from((View) view.getParent());

        return dialog;
    }

    public void show(final FragmentActivity fragmentActivity) {
        show(fragmentActivity.getSupportFragmentManager(), TAG);
    }
}

像正常调用一样关闭对话框close().