css - 绘制三角形

/*向上*/
#triangle-up {
width: 0;
height: 0;
border-left: 50px solid transparent;
border-right: 50px solid transparent;
border-bottom: 100px solid red;
}
/*向下*/
#triangle-down {
width: 0;
height: 0;
border-left: 50px solid transparent;
border-right: 50px solid transparent;
border-top: 100px solid red;
}
/*向左*/
#triangle-left {
width: 0;
height: 0;
border-top: 50px solid transparent;
border-right: 100px solid red;
border-bottom: 50px solid transparent;
}
/*向右*/
#triangle-right {
width: 0;
height: 0;
border-top: 50px solid transparent;
border-left: 100px solid red;
border-bottom: 50px solid transparent;
}
/*左上*/
#triangle-topleft {
width: 0;
height: 0;
border-top: 100px solid red;
border-right: 100px solid transparent;
}
/*右上*/
#triangle-topright {
width: 0;
height: 0;
border-top: 100px solid red;
border-left: 100px solid transparent;
}
/*左下*/
#triangle-bottomleft {
width: 0;
height: 0;
border-bottom: 100px solid red;
border-right: 100px solid transparent;
}
/*右上*/
#triangle-bottomright {
width: 0;
height: 0;
border-bottom: 100px solid red;
border-left: 100px solid transparent;
}