css实现的信封

<div class="mail icon"></div>

.mail.icon:before {
  content: '';
  position: absolute;
  left: 7px;
  top: -4px;
  width: 1px;
  height: 10px;
  background-color: currentColor;
  -webkit-transform-origin: bottom;
          transform-origin: bottom;
  -webkit-transform: rotate(-54deg);
          transform: rotate(-54deg);
}
.mail.icon:after {
  content: '';
  position: absolute;
  left: 7px;
  top: -4px;
  width: 1px;
  height: 10px;
  background-color: currentColor;
  -webkit-transform-origin: bottom;
          transform-origin: bottom;
  -webkit-transform: rotate(54deg);
          transform: rotate(54deg);
}