メールのアイコン

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

.dli-mail {
  display: inline-block;
  vertical-align: middle;
  color: #333;
  line-height: 1;
  position: relative;
  width: 1.06667em;
  height: 0.8em;
  border: 0.1em solid currentColor;
  border-radius: 0.1em;
  box-sizing: content-box;
  overflow: hidden;
}

.dli-mail::before {
  content: '';
  position: absolute;
  left: 50%;
  top: 0;
  width: 0.75425em;
  height: 0.75425em;
  border: 0.1em solid currentColor;
  border-top-color: transparent;
  border-right-color: transparent;
  border-radius: 0 0 0 0.1em;
  box-sizing: content-box;
  transform: translate(-50%, -50%) rotate(-45deg) skew(10deg, 10deg);
}