1，index.html
<!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>Document</title>
<link rel="stylesheet" href="style.css">
</head>
<body>
<div class="box">
<div class="content">
<h1>HTML5 简介</h1>
<p>HTML5是HTML最新的修订版本，2014年10月由万维网联盟（W3C）完成标准制定。
HTML5的设计目的是为了在移动设备上支持多媒体。
HTML5 简单易学。</p>
</div>
</div>
</body>
</html>
2，style.css
@import url('http://fonts.googleapis.com/css?family=Poppins:100,200,300,400,500,600,700,800,900');
body{
margin: 0;
padding: 0;
display: flex;
align-items: center;
justify-content: center;
min-height: 100vh;
background: #060c21;
font-family: 'Poppins',sans-serif;
}
.box{
position: relative;
300px;
height: 400px;
display: flex;
justify-content: center;
align-items: center;
background: #060c21;
}
.box:before{
content: '';
background: #fff;
position: absolute;
top: -2px;
bottom: -2px;
left: -2px;
right: -2px;
z-index: -1;
}
.box:after{
content: '';
background: #fff;
position: absolute;
top: -2px;
bottom: -2px;
left: -2px;
right: -2px;
z-index: -2;
filter: blur(40px)
}
.box:before,.box:after{
background: linear-gradient(235deg,#89ff00,#060c21,
#00bcd4)
}
.content{
padding: 20px;
box-sizing: border-box;
color: #fff;
}