add_action( 'widgets_init', 'custom_register_widget_areas' );
function custom_register_widget_areas() {
  register_sidebar(
    array(
      'name'          => esc_html__( 'Fullscreen Menu Widgets', 'rubenz' ),
      'id'            => 'header-sidebar',
      'description'   => esc_html__( 'Appears on desktop in the page header if menu type is set to "fullscreen".', 'rubenz' ),
      'before_widget' => '<div class="header__wrapper-property"><div class="figure-property"><div class="widget widget_%2$s split-text">',
      'after_widget'  => '</div></div></div>',
      'before_title'  => '<div class="figure-property__wrapper-heading"><h6 class="widgettitle split-text">',
      'after_title'   => '</h6></div>',
    )
  );
}