​x
 
<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<style>
/* 针对宽度小于 400 像素的设备： */
body {
  background-repeat: no-repeat;
  background-image: url('/i/photo/tulip_peach_blossom_s.jpg'); 
}
​
/* 针对宽度大于等于 400 像素的设备： */
@media only screen and (min-device-width: 400px) {
  body { 
     background-image: url('/i/photo/flower-5.jpg'); 
  }
}
</style>
</head>
<body>
​
</body>
</html>
​