Code input fields can be created with the following configuration:
'additionalCss' => [ 'type' => 'code', 'language' => 'css', 'panel' => 'custom_code', 'value' => $options['additionalCss'] ?? '', 'label' => esc_html__( 'Additional CSS', 'fieldify' ), 'description' => esc_html__( 'Add additional CSS to your site.', 'fieldify' ), 'placeholder' => '', 'rows' => 12, 'permission' => 'administrator',]