rem为所有屏幕设置初始font-size

<script> (function (doc, win) { var docEl = doc.documentElement, resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize', recalc = function () { var clientWidth = docEl.clientWidth; if (!clientWidth) return; docEl.style.fontSize = 20 * (clientWidth / 320) + 'px'; };   if (!doc.addEventListener) return; win.addEventListener(resizeEvt, recalc, false); doc.addEventListener('DOMContentLoaded', recalc, false); })(document, window); </script>