HTML清楚塌陷问题

/* 清除浮动塌陷问题 */
.clearfix:after {
 clear: both;
}

.clearfix:after,
.clearfix:before {
 content: " ";
 display: table;
}

/* 清除浮动塌陷问题 */
.clearfix:after {
	clear: both;
}

.clearfix:after,
.clearfix:before {
	content: " ";
	display: table;
}