The best way to outline a Block Fashion in an Innerblocks template

I am constructing a Innerblocks block template (in PHP) with the next syntax:

$template = [
    [
        'core/heading', 
        [
          'level' => 1,
          'content' => 'Example Heading.',
          'align' => 'center'
        ],
    ],
  [
        'core/button', 
        [
          'text' => 'Button 1',
          'align' => 'center',
          'style' => 'outline', // <-- this doesn't work
        ],
    ]
];

It largely works as anticipated, however I am unable to decide the syntax to make use of (or whether it is even supported) to outline the blocks’ fashion. For instance, I would really like the Button to make use of the "Outline" fashion as an alternative of its default "Fill" fashion. I’ve tried as proven above, and likewise tried one thing like: kinds => ['name' => 'outline'] to echo the construction of the core/buttons object, however neither work.