Change color of the + – icon
.pt-cv-collapsible .panel-heading span .glyphicon {color: YOUR_COLOR !important;}
Remove the border and box shadow around item
.pt-cv-collapsible .panel {border: none !important; box-shadow: none !important;}
Remove the border under the Title
.pt-cv-collapsible .panel-group .panel-heading+.panel-collapse .panel-body {border-top: none !important;}
Change the color of the border under the Title
.pt-cv-collapsible .panel-group .panel-heading+.panel-collapse .panel-body {border-top: 1px solid YOUR_COLOR !important;}
Rounded corners
.pt-cv-collapsible .panel {border-radius:5px !important}
Best regards,