写border的样式
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>CSS样式</title>
<style>
.mr{margin: 0 auto;}
body{background: salmon;}
.bt1{width:250px; height: 250px; border: 2px dashed #000000; border-radius: 50%;}
.bt2{width:500px; height: 250px; border-bottom: 2px solid #ffff; border-top:2px solid #ff6500;}
button{border: none;text-align:center; width:100px; height: 35px;}
.bt3{width:500px; height: 250px; margin-top:5px; box-shadow:0px 5px 30px #fff; margin: 0 auto;}
</style>
</head>
<body >
<div class="bt1 mr"></div>
<div class="bt2 mr"></div>
<button >提交按钮</button>
<div class="bt3"></div>
</body>
</html>