フォルダのアイコン

<span class="dli-folder"><span></span></span>

.dli-folder {
  display: inline-block;
  vertical-align: middle;
  color: #333;
  line-height: 1;
  position: relative;
  width: 1.25em;
  height: 0.75em;
  border: 0.1em solid currentColor;
  border-radius: 0 0.1em 0.1em 0.1em;
  background: #fff;
  box-sizing: content-box;
}

.dli-folder > span {
  position: absolute;
  left: -0.1em;
  bottom: 100%;
  width: 0.5em;
  height: 0.15em;
  background: #fff;
  border: 0.1em solid currentColor;
  border-right: 0;
  border-bottom: 0;
  border-radius: 0.1em 0.1em 0 0;
  box-sizing: content-box;
}

.dli-folder > span::before {
  content: '';
  position: absolute;
  top: -0.1em;
  left: calc(100% - 0.1em);
  width: 0.175em;
  height: 0;
  border-top: 0.1em solid currentColor;
  transform: rotate(55deg);
  transform-origin: left bottom;
  box-sizing: content-box;
}