Edit in JSFiddle

.close {
  width: 50px;
  height: 50px;
  opacity: 0.8;
}

.close:before, .close:after {
  position: absolute;
  left: 15px;
  content: ' ';
  height: 40px;
  width: 2px;
  background-color: #000;
}
.close:before {
  transform: rotate(45deg);
}
.close:after {
  transform: rotate(-45deg);
}

<div class="close"></div>