Using Pure CSS to create "X" and "/"

For creating “X”

HTML

<a href="#" class="close">

CSS

.close {
  position: absolute;
  right: 32px;
  top: 32px;
  width: 32px;
  height: 32px;
  opacity: 0.3;
}
.close:hover {
  opacity: 1;
}
.close:before, .close:after {
  position: absolute;
  left: 15px;
  content: ' ';
  height: 33px;
  width: 2px;
  background-color: #333;
}
.close:before {
  transform: rotate(45deg);
}
.close:after {
  transform: rotate(-45deg);
}

For creating “/”

HTML

<a href="#" class="close">

CSS

.close {
  position: absolute;
  right: 32px;
  top: 32px;
  width: 32px;
  height: 32px;
  opacity: 0.3;
}
.close:hover {
  opacity: 1;
}
.close:before {
  position: absolute;
  left: 15px;
  content: ' ';
  height: 33px;
  width: 2px;
  background-color: #333;
}
.close:before {
  transform: rotate(45deg);
}

Reference check