css写出三角形（兼容IE）

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; 
    }

效果如下：