rem自适应

        (function  response() {
            //基准320
            let doc = document.documentElement, win = window;

            recale = function () {
                let fsize = 20*(doc.clientWidth/320);
                doc.style.fontSize = fsize+'px';
            }
            doc.addEventListener('DOMContentLoaded',recale,false);  // 监听函数的兼容性未考虑
            //win.addEventListener('orientationchange',recale,false)  监听屏幕方向变化  横屏与竖屏
            win.addEventListener('resize',recale,false);
        })()