after - clear: both

<style>
	.example {
		padding: 16px;
		border: 4px solid red;
	}
	.clearfix:after {
		content: "";
		display: block;
		clear: both;
	}
	.example .box {
		border: 2px solid blue;
	}
	.example .left {
		float: left;
		width: 250px;
		height: 60px;
	}
	.example .right {
		float: right;
		width: 400px;
		height: 80px;
	}
</style>

<div class="example clearfix">
	<div class="box left">float: left;</div>
	<div class="box right">float: right;</div>
</div>