function theme_options_metabox($metabox_id, $key) {

    $prefix = 'theme';
    $cmb_options = new_cmb2_box( array(
        'id'      => $metabox_id,
        'title'   => 'Theme Options',
        'hookup'  => false,
        'show_on' => array(
            'key'   => 'options-page',
            'value' => array( $key )
        )
    ) );

    $group_field_id = $cmb_options->add_field( array(
        'id'          => $prefix . 'demo',
        'type'        => 'group',
        'description' => __( 'Generates reusable form entries', 'cmb2' ),
        'options'     => array(
            'group_title'   => __( 'Entry {#}', 'cmb2' ),
            'add_button'    => __( 'Add Another Entry', 'cmb2' ),
            'remove_button' => __( 'Remove Entry', 'cmb2' ),
            'sortable'      => true,
        ),
    ) );

    $cmb_options->add_group_field( $group_field_id, array(
        'name'       => __( 'Entry Title', 'cmb2' ),
        'id'         => 'title',
        'type'       => 'text',
    ) );
}