A reference to i/icons/ in the css
In the console I see it can't find https://EXAMPLE.org/civicrm_custom/extensions/contrib/finsburypark/i/icons/jquery-ui-3E3E3E.png
. Perhaps it should be https://EXAMPLE.org/civicrm_custom/extensions/contrib/finsburypark/images/jquery-ui-3E3E3E.gif
. (By the way in Drupal 9 with CiviCRM it copies all these assets to /libraries/civicrm/finsburypark/
as well but the path to the extension can still be used).