//px转换rem /50
        (function (doc, win) {
            var docEl = doc.documentElement,
                resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',
                recalc = function () {
                    var clientWidth = docEl.clientWidth > 750 ? 750 : docEl.clientWidth;
                    if (!clientWidth) return;
                    docEl.style.fontSize = 50 * (clientWidth / 750) + 'px';
                };
            if (!doc.addEventListener) return;
            win.addEventListener(resizeEvt, recalc, false);
            doc.addEventListener('DOMContentLoaded', recalc, false);
        })(document, window);