rem

       (function (doc, win) {
            var docEl = doc.documentElement;
            var resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize';
            var reCalc = function () {
                var clientWidth = docEl.clientWidth;
                if (!clientWidth) return;
                win.baseFontSize = 100 * (clientWidth / 375);
                docEl.style.fontSize = win.baseFontSize + 'px'
            };
            if (!doc.addEventListener) return;
            reCalc();
            win.addEventListener(resizeEvt, reCalc, false);
            doc.addEventListener('DOMContentLoaded', reCalc, false)
        })(document, window);