function mytheme_register_meta_boxes( $meta_boxes ){
    $prefix = 'mytheme';

    // Page builder
    $meta_boxes[] = array(
        'id'       => $prefix . 'page_builder',
        'title'    => esc_html__( 'Page Builder', 'mytheme' ),
        'pages'    => array( 'page' ),
        'context'  => 'normal',
        'priority' => 'high',
        'show'     => array(
            'template'    => array( 'page-builder.php' ),
        ),

        'fields' => array(
            array(
                'id'            => $prefix . 'section',
                'type'          => 'group',
                'collapsible'   => true,
                'clone'         => true,
                'group_title'   => array(
                    'field'     => 'section-select',
                ),
                'sort_clone'    => true,
                'save_state'    => true,
                // List of sub-fields
                'fields' => array(
                    array(
                        'name'          => esc_html__('Section', 'mytheme'),
                        'id'            => 'section-select',
                        'type'          => 'select',
                        'placeholder'   => esc_html__( 'Select a layout', 'mytheme' ),
                        'options'       => array(
                            'fullwidth' => esc_html__( 'Fullwidth Section', 'mytheme' ),
                            'with-sidebar' => esc_html__( 'With Sidebar Section', 'mytheme' ),
                        ),
                    ),
                    array(
                        'id'            => $prefix . 'section-main-col',
                        'type'          => 'group',
                        'collapsible'   => true,
                        'clone'         => true,
                        'group_title'   => array(
                            'field'     => 'section-main-col-select',
                        ),
                        'sort_clone'    => true,
                        'save_state'    => true,
                        // List of sub-fields
                        'fields'        => array(
                            array(
                                'name'          => esc_html__('Section', 'mytheme'),
                                'id'            => 'section-main-col-select',
                                'type'          => 'select',
                                'placeholder'   => esc_html__( 'Select a layout', 'mytheme' ),
                                'options'       => array(
                                    'posts-listing' => esc_html__( 'Posts Listing', 'mytheme' ),
                                    'slider' => esc_html__( 'Slider', 'mytheme' ),
                                ),
                            ),
                        ),
                    ),
                ),
            ),

        ),
    );

    return $meta_boxes;
}