css3 画三角形

/*箭头向上*/

.arrow-up {
0;
height:0;
border-left:20px solid transparent;
border-right:20px solid transparent;
border-bottom:20px solid #000;
}

/*箭头向下*/
.arrow-down {
0;
height:0;
border-left:20px solid transparent;
border-right:20px solid transparent;
border-top:20px solid #0066cc;
}

/*箭头向左*/
.arrow-left {
0;
height:0;
border-top:20px solid transparent;
border-bottom:20px solid transparent;
border-right:20px solid yellow;
}

/*箭头向右*/
.arrow-right {
0;
height:0;
border-top:20px solid transparent;
border-bottom: 20px solid transparent;
border-left: 20px solid green;
}