CSS如何让不相等的字符上下对齐

<div class="main">
      <span style="font-size:12px;"><dl class="hotsearch" style="width:300px;">
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  <style type="text/css">
    .hotsearch dd{
      float: left;
      line-height: 24px;
      margin-right: 30px;
      overflow: hidden;
      text-align: center;
      width: 4em; /*这个值是看最长能显示几个文字，如x，则为x em*/
    }
    .hotsearch dd a{
      display:block;
    }
    .w2{
      letter-spacing:2em; /*如果需要y个字两端对齐，则为(x-y)/(y-1),这里是（4-2）/(2-1)=2em */
      margin-right:-2em; /*同上*/
    }
    .w3{
      letter-spacing:0.5em; /*如果需要y个字两端对齐，则为(x-y)/(y-1),这里是（4-3）/(3-1)=0.5em */
      margin-right:-0.5em; /*同上*/
    }
    </style>