Function to add Widget class to it’s parent

For styling reasons I need the Widget class entered under the Attributes tab of a widget also in the parent div (The div with class .so-panel).

I know you can add the Row class to it’s parent with the following function:

function panels_row_classes( $classes, $grid ) {
	$classes[] = $grid["style"]["class"];
	return $classes;
}
add_filter( 'siteorigin_panels_row_classes', 'panels_row_classes', 10, 2 );

Now I also need something simular for the Widget class, but my knowledge of Filters and Hooks are limited.

Any help is appreciated!