/* body */

div.square{
	width: 400px;
	height: 200px;
	background-color: #ccc;
	
	/* 方案一
	position: absolute;
	top: 0;
	right: 0;
	left: 0;
	bottom: 0;
	margin: auto;*/
	
	/* 方案二*/
	position: absolute;
	top: 50%;
	left: 50%;
	margin-left: -200px;
	margin-top: -100px;
}

div.circle1,div.circle2{
	background-color: #fc0;
	width: 50px;
	height: 50px;	
}

div.circle1{
	border-bottom-right-radius: 100%;
}
div.circle2{
	border-top-left-radius: 100%;
	margin: 100px 0 0 350px;
}