css写出三角形
利用css写三角形，兼容IE7
.arrow-up {
width:0px;
height:0px;
border-left:10px solid transparent;
border-right:10px solid transparent;
border-bottom:10px solid red;
font-size:0px;
line-height:0px;
margin: 0 auto;
}
.arrow-down {
width:0px;
height:0px;
border-left:10px solid transparent;
border-right:10px solid transparent;
border-top:10px solid blue;
font-size:0px;
line-height:0px;
}
.arrow-left {
width:0px;
height:0px;
border-bottom:10px solid transparent;
border-top:10px solid transparent;
border-right:10px solid #DC143C;
font-size:0px;
line-height:0px;
}
.arrow-right {
width:0px;
height:0px;
border-bottom:10px solid transparent;
border-top:10px solid transparent;
border-left:10px solid #FF00FF;
font-size:0px;
line-height:0px;
}