根據屏幕分辨率設置1rem相對應的px

(function(doc, win) {
    var docEl = doc.documentElement,
        resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',
        recalc = function() {
            var clientWidth = docEl.clientWidth;
            if (!clientWidth) return;
            if(clientWidth>=1280){
                docEl.style.fontSize = 100 * (clientWidth / 1920) + 'px';
            }else {
                docEl.style.fontSize = 100 * (1280 / 1920) + 'px';
            }
        };
    if (!doc.addEventListener) return;
    win.addEventListener(resizeEvt, recalc, false);
    doc.addEventListener('DOMContentLoaded', recalc, false);
})(document, window);