#colorbox #cboxClose {
  display: block !important;
  position: absolute;
  top: 5px;
  right: 5px;
  z-index: 9999;
  background: transparent;
  color: #fff;
  font-size: 24px;
  font-weight: bold;
  cursor: pointer;
}

#colorbox #cboxClose::before {
  content: "×"; /* fancy 'X' */
}