Render arrays are great for styling elements to keep consistency across future updates. Today: buttons.
$inviteButton = [
'#type' => 'button',
'#value' => t('Invite contact person'),
'#attributes' => [
'class' => ['button', 'button--action', 'button--small', 'button--danger'],
],
];
return [
'#markup' => Markup::create(render($inviteButton)),
];
This will look like this: