Html CSS和浮动中的浮动

在下面的示例中，是否有人知道如何并排放置两个重复元素：

.thumbnail {
  float: left;
  width: 30px;
  border: 1px solid #999;
  margin: 0 15px 15px 0;
}
.clearboth { clear:both; }


<!-- repeating element -->
<div class="thumbnail">1A</div>
<div class="thumbnail">1B</div>
<div class="thumbnail">1C</div>
<br class="clearboth">
<div class="thumbnail">2A</div>
<div class="thumbnail">2B</div>
<div class="thumbnail">2C</div>
<br class="clearboth">

<!-- repeating element -->
<div class="thumbnail">1A</div>
<div class="thumbnail">1B</div>
<div class="thumbnail">1C</div>
<br class="clearboth">
<div class="thumbnail">2A</div>
<div class="thumbnail">2B</div>
<div class="thumbnail">2C</div>
<br class="clearboth">

缩略图{
浮动：左；
宽度：30px；
边框：1px实心#999；
利润率：0 15px 15px 0；
}
.clearTheals{clear:tweals；}
1A
1B
1C


2A
2B
2C


1A
1B
1C


2A
2B
2C

诀窍是我已经在使用float和clear属性来分别设置每个重复元素的样式。但是当在浮动元素中嵌套浮动元素时，它不起作用

看看这个

<!-- repeating element -->
<div id="first">
<div class="thumbnail">1A</div>
<div class="thumbnail">1B</div>
<div class="thumbnail">1C</div>
<br class="clearboth">
<div class="thumbnail">2A</div>
<div class="thumbnail">2B</div>
<div class="thumbnail">2C</div>
<br class="clearboth">
</div>    
<!-- repeating element -->
<div id="second">    
<div class="thumbnail">1A</div>
<div class="thumbnail">1B</div>
<div class="thumbnail">1C</div>
<br class="clearboth">
<div class="thumbnail">2A</div>
<div class="thumbnail">2B</div>
<div class="thumbnail">2C</div>
<br class="clearboth">
</div>

看看这个

<!-- repeating element -->
<div id="first">
<div class="thumbnail">1A</div>
<div class="thumbnail">1B</div>
<div class="thumbnail">1C</div>
<br class="clearboth">
<div class="thumbnail">2A</div>
<div class="thumbnail">2B</div>
<div class="thumbnail">2C</div>
<br class="clearboth">
</div>    
<!-- repeating element -->
<div id="second">    
<div class="thumbnail">1A</div>
<div class="thumbnail">1B</div>
<div class="thumbnail">1C</div>
<br class="clearboth">
<div class="thumbnail">2A</div>
<div class="thumbnail">2B</div>
<div class="thumbnail">2C</div>
<br class="clearboth">
</div>