研究了一天多的rem終於有了眉目，下面來說一說

其實我一直糾結的是在react專案中在那裡設定rem與px的對應關係

react中在index.html中把下面這段已壓縮過的 原生JS放在scrip中

  !function (e) { function t(a) { if (i[a]) return i[a].exports; var n = i[a] = { exports: {}, id: a, loaded: !1 }; return e[a].call(n.exports, n, n.exports, t), n.loaded = !0, n.exports } var i = {}; return t.m = e, t.c = i, t.p = "", t(0) }([function (e, t) { "use strict"; Object.defineProperty(t, "__esModule", { value: !0 }); var i = window; t["default"] = i.flex = function (e, t) { var a = e || 100, n = t || 1, r = i.document, o = navigator.userAgent, d = o.match(/Android[\S\s]+AppleWebkit\/(\d{3})/i), l = o.match(/U3\/((\d+|\.){5,})/i), c = l && parseInt(l[1].split(".").join(""), 10) >= 80, p = navigator.appVersion.match(/(iphone|ipad|ipod)/gi), s = i.devicePixelRatio || 1; p || d && d[1] > 534 || c || (s = 1); var u = 1 / s, m = r.querySelector('meta[name="viewport"]'); m || (m = r.createElement("meta"), m.setAttribute("name", "viewport"), r.head.appendChild(m)), m.setAttribute("content", "width=device-width,user-scalable=no,initial-scale=" + u + ",maximum-scale=" + u + ",minimum-scale=" + u), r.documentElement.style.fontSize = a / 2 * s * n + "px" }, e.exports = t["default"] }]);  flex(100, 1);

這裡1rem=100px

然後在根據設計圖進行單位換算