プラス、＋、追加（丸囲み）のアイコン

<span class="dli-plus-circle"><span></span></span>

.dli-plus-circle {
  display: inline-block;
  vertical-align: middle;
  color: #333;
  line-height: 1;
  position: relative;
  width: 1em;
  height: 1em;
  border: 0.1em solid currentColor;
  border-radius: 50%;
  box-sizing: content-box;
}

.dli-plus-circle > span {
  width: 52%;
  height: 0.1em;
  background: currentColor;
  border-radius: 0.1em;
  position: relative;
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  margin: auto;
}

.dli-plus-circle > span::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: inherit;
  border-radius: inherit;
  transform: rotate(90deg);
}