分兩種情況：

.content{
  width:350px;
  height:150px;
	color:#fff;
}
.content1,.content2{
	background-color: #00f;
}
.content2{
	margin-top:10px;
}
.one{
	background-color:#f00;
	float: left;

}
.two{
	background-color: #3dfeca;
}
.content1 .one,
.content2 .one{
	height:50px;
}

一，後面的元素是塊級元素---block

<div class=‘content content1‘>
    	<div class=‘one‘>
		the folowing element is block;
	</div>
	<div class=‘two‘>
		second div idv idv div div div div div div div div
	</div>
 </div>

二，後面的元素是行內元素--inline

1 <div class=‘content content2‘>
2     <div class=‘one‘>
3     the folowing element is inline;
4     </div>
5     <span class=‘two‘>
6         inline element is span;there is other inline element such as a,i,b,em
7     </span>
8 </div>    

元素設置float屬性後，其後面的元素的位置問題