CSS优先级

<div class="time-top">
<dl>
<dd>0</dd>
<dd>6</dd>
<dd class="no">:</dd>
<dd>4</dd>
<dd>9</dd>
<dd class="no">:</dd>
<dd>0</dd>
<dd>8</dd>
</dl>
</div>

.time-top .no{       /* 此处必须有父级 .time-top 类选择器，否则只是 .no 的话不起作用 */
color: #555555;
background: #FFECBF;
font-weight: bold;
font-size: 18px;
font-family: "宋体";
margin: 0;
width: 16px;
}
.time-top dd{
font-weight: bold;
font-family: "宋体";
display: block;
font-size: 20px;
color: #FFF;
float: left;
text-align: center;
width: 20px;
height: 28px;
background: url("images/indexsprite.png") no-repeat -83px -77px;
margin: 0 2px 0 0;
}