add_action('product_designer_panel', 'product_designer_panel_20200808', 0);
function product_designer_panel_20200808($atts){
$settings = isset($atts['settings']) ? $atts['settings'] : array();
$menu_position = isset($settings['menu_position']) ? $settings['menu_position'] : 'left';
$icons = isset($atts['icons']) ? $atts['icons'] : '';
$cube = isset($icons['cube']) ? $icons['cube'] : '';
?>
<p>Custom html</p>
<?php
}