CSS 画三角形

#triangle-up {
  	width: 0;
  	height: 0;
  	border-left: 50px solid transparent;
  	border-right: 50px solid transparent;
  	border-bottom: 100px solid red;
}

#triangle-down {
	width: 0;
  	height: 0;
  	border-left: 50px solid transparent;
  	border-right: 50px solid transparent;
  	border-top: 100px solid red;
}

#triangle-left {
  width: 0;
  height: 0;
  border-top: 50px solid transparent;
  border-right: 100px solid red;
  border-bottom: 50px solid transparent;
}

#triangle-right {
  width: 0;
  height: 0;
  border-top: 50px solid transparent;
  border-left: 100px solid red;
  border-bottom: 50px solid transparent;
}

#triangle-topleft {
  width: 0;
  height: 0;
  border-top: 100px solid red;
  border-right: 100px solid transparent;
}

#triangle-topright {
  width: 0;
  height: 0;
  border-top: 100px solid red;
  border-left: 100px solid transparent;
}

#triangle-bottomleft {
  width: 0;
  height: 0;
  border-bottom: 100px solid red;
  border-right: 100px solid transparent;
}

#triangle-bottomright {
  width: 0;
  height: 0;
  border-bottom: 100px solid red;
  border-left: 100px solid transparent;
}