rem样板

window.onload=window.onresize=function(){
    var rem=document.documentElement.clientWidth*20/320;
    document.documentElement.style.fontSize = rem+'px';
};

meta标签：

<meta name="viewport"
          content="width=device-width, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0, user-scalable=no">