9、三角箭头

1.三角箭头

div{
  width: 0;
  height: 0;
  border: 10px solid #fff;
  border-right-color: #000;
}

2.用css写三角

body{
  background-color:#fff;
}
div{
  width: 0;
  height: 0;
  border:10px solid transparent;
  border-bottom-color:#000 ;
  position: relative;
}
div::after{
  content: "";
  display: block;
  width: 0;
  height: 0;
  border: 8px solid transparent;
  border-bottom-color: #fff;
  position: absolute;
  left: 50%;
  margin-left: -8px;
  top: -5px;
}