overflow解决浮动高度塌陷问题的原理--触发BFC

<div class="div">
	<div></div>
		</div>

<pre name="code" class="html"><style type="text/css">
			.div{
				width: 600px;
				border:5px solid black;
				overflow: hidden;
			}
			div{
				width: 400px;
				height: 200px;
				background: blue;
				float: left;
			}
		</style><p