<!DOCTYPE html>
<html>
<head lang="en">
<meta charset="UTF-8">
<title></title>
<style>
.sx{
float:left;
margin-top: 30px;
width: 1px;
height: 400px;
background: darkgray;
margin-left: 800px;
}
</style>
</head>
<body>
<div class="sx"></div>
</body>
</html>
效果
