css rem 使用方法

var firstSize = getComputedStyle(document.getElementsByTagName("html")[0])["fontSize"]
var mresize=function(){
    var view_width =window.innerWidth;
    var path=  firstSize;
    path=path.substring(0,path.length-2);
    var n =view_width/path;
    document.getElementsByTagName("html")[0].style["font-size"] = n+"px";
};
mresize();
window.onresize = function() {
    mresize()
};