大屏展示中，这样用rem

(function (doc, win) {
    var docEl = doc.documentElement,
        resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',
        recalc = function () {
            var clientWidth = docEl.clientWidth;
            if (!clientWidth) return;
            if (clientWidth >= 1920) {
                docEl.style.fontSize = '100px'; //1rem  = 100px
            } else {
                docEl.style.fontSize = 100 * (clientWidth / 1920) + 'px';
            }        
};    
if (!doc.addEventListener) return;
    win.addEventListener(resizeEvt, recalc, false);
    doc.addEventListener('DOMContentLoaded', recalc, false);
})(document, window);

此代码应该放在引入css之前。