.icon-x {
  width: 40px;
  height: 40px;
  display: block;
  position: relative;
}
.icon-x:before,
.icon-x:after {
  -webkit-transition: all 0.3s ease;
  transition: all 0.3s ease;
  content: '';
  position: absolute;
  width: 40px;
  top: 50%;
  height: 1px;
  background: #888;
  -webkit-transform: rotate(45deg);
          transform: rotate(45deg);
}
.icon-x:after {
  -webkit-transform: rotate(-45deg);
          transform: rotate(-45deg);
}