矢印

<span class="arrow"></span>

.arrow{
  display: inline-block;
  width: 0;
  height: 0;
  border-top: transparent 40px solid;
  /* border-top: red 40px solid; */
  border-right: green 40px solid;
  border-bottom: blue 40px solid;
  border-left: orange 40px solid;
}