<html>
	<head>
		<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
		<title>CSS绝对定位</title>
		<style type="text/css">
			div{
				background-color: Red;
				width: 30px;
				height: 30px;
			}

			#box_relative {
				position: absolute;
				left: 20px;
				top: 20px; background-color: gray;
			}
		</style>
	</head>
	<body>
		<div style="z-index:30"></div><div id="box_relative"></div><div style="z-index:30"></div>
	</body>
</html>

运行结果
在这里插入图片描述