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<?php

//NEW
add_shortcode('custom_shopicon', 'custom_shopicon_shortcode');
function custom_shopicon_shortcode($atts = [], $content = null) {

  shortcode_atts(array(
      'title' => '',
      'subtitle' => '',
  ), $atts);

  if(empty($atts)) $atts = array();
  if(!isset($atts['title'])) $atts['title'] = 'Rozwiń';
  if(!isset($atts['subtitle'])) $atts['subtitle'] = 'Zwiń';
  
  ob_start(); ?>
  
  <?php $output = ob_get_contents(); ob_end_clean();
  return $output;
}