.fl-node- .fl-accordion-item:not(:last-child) {
	border-bottom: none;
	border-bottom-left-radius: 0;
	border-bottom-right-radius: 0;
}
.fl-node- .fl-accordion-item:not(:first-child) {
	border-top-left-radius: 0;
	border-top-right-radius: 0;
}

<br />
<b>Fatal error</b>:  Uncaught Error: Class 'FLBuilderCSS' not found in /home/modular/gites-douelafontaine.fr/httpdocs/wp-content/plugins/bb-plugin/modules/accordion/includes/frontend.css.php:26
Stack trace:
#0 {main}
  thrown in <b>/home/modular/gites-douelafontaine.fr/httpdocs/wp-content/plugins/bb-plugin/modules/accordion/includes/frontend.css.php</b> on line <b>26</b><br />