Dcat-Admin/resources/assets/dcat/sass/components/_icon-picker.scss

.iconpicker-popover.popover .popover-title {
  background: #fff!important;
}

.iconpicker-popover.popover.bottom>.arrow, .iconpicker-popover.popover.bottomRight>.arrow, .iconpicker-popover.popover.bottomLeft>.arrow {
  border-bottom-color: #dfdfdf!important;
}