@media screen

<! DOCTYPE HTML PUBLIC "-//w3c//dtd HTML 4.01 transitional//en" "HTTP://WWW.W3.ORG/TR/HTML4/LOOSE.DTD" >

<meta charset= "gb2312" >
<title> New Document </title>
<meta name= "Keywords" content= "" >
<meta name= "Description" content= "" >
<meta http-equiv= "x-ua-compatible" content= "Ie=edge" >
<meta name= "viewport" content= "initial-scale=1, maximum-scale=1, User-scalable=no" >

<style>
P{display:none}
Body{background-color:red}
@media screen and (max-width:320px) {#ip4 {display:block;} Body{background-color:blue}}
</style>
<body>
<p id= "IP4" > Apple 4</p>
<p id= "IP5" > Apple 5</p>
<p id= "IP6" > Apple 6</p>
<p id= "ip6+" > Apple 6+</p>
<script>
Document.documentElement.style.height = window.innerheight + ' px ';
alert (document.documentElement.clientWidth);
alert (document.documentElement.style.height);
</script>
</body>

@media screen