【CSS】プラスとマイナスをつくる

<div class="plus"></div>

.plus {
  position: relative;
  width: 30px;
  height: 30px;
  margin: 0 5px;
}
.plus:before, .plus:after {
  display: block;
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  margin: auto;
  background-color: #333;
  border-radius: 10px;
}
.plus:before {
  width: 5px;
  height: 30px;
}
.op_plus:after {
  width: 30px;
  height: 5px;
}

<div class="minus"></div>

.minus {
  position: relative;
  width: 30px;
  height: 30px;
  margin: 0 5px;
}
.minus:after {
  display: block;
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  margin: auto;
  background-color: #333;
  border-radius: 10px;
  width: 30px;
  height: 5px;
}