このサイトのコードコピペで簡単！！
http://ringo-12.com/%E5%B0%8F%E6%8A%80/4950
.my_ranking {
counter-reset: wpp-ranking;
}
.my_ranking ul li{
position:relative;
}
.my_ranking ul li:before {
color:#FFF;
content: counter(wpp-ranking, decimal);
counter-increment: wpp-ranking;
text-align:center;
opacity:0.999;
line-height: 21px;
width: 20px;
height: 20px;
background-color:#5e9ab5;
border-radius: 2px;
position: absolute;
left: 0;
top: 0;
}
