css代码如下：
<!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>
<style>
#div1 {
width: 200px;
height: 200px;
border: 1px solid #333;
background: -webkit-linear-gradient(top,red,yellow); /* chrome */
background: -ms-linear-gradient(top,red,yellow); /* IE10及以上 */
background: -moz-linear-gradient(top,red,yellow); /* 火狐 */
background: linear-gradient(top,red,yellow); /* 兼容 */
}
</style>
</head>
<body>
<div id="div1"></div>
</body>
</html>
效果如下：
