<link rel="stylesheet" media="screen and (max-width: 1024px)" href="middle.css" />

<link rel="stylesheet" media="screen and (max-width: 600px)" href="small.css" />

.first {background-color: white;}
.second {background-color: black;}

@media screen and (max-width: 800px) {
 /*当屏幕尺寸小于800px时，应用下面的CSS样式*/
    .first {background-color: green;}
    .second {background-color: skyblue;}
}

@media screen and (max-width: 480px) {
 /*当屏幕尺寸小于480px时，应用下面的CSS样式*/
    .first {background-color: yellow;}
    .second {background-color: red;}
}