em{
width:20px;
text-align:center;
height:16px;
line-height:16px;
font-size:12px;
font-style:normal;
background:url( "http://img1.sycdn.imooc.com//53cf0fa20001d3dc00200032.jpg") no-repeat;
background-position:bottom;
margin:3px;
color:#333;
float:left;
}