h5 1rem=100px

!function(win,doc){

            win.onload = function(){

                const PXSTANDARD = 375, REMUNIT = 100;

                var ST = null, winWidth = 0;

                win.addEventListener("resize",function(){

                    clearTimeout(ST)

                    ST = setTimeout(function(){

                        setBodyFontSize();

                    },60);

                })

                function setBodyFontSize(){

                    winWidth = win.innerWidth;

                    doc.documentElement.style.fontSize = winWidth/PXSTANDARD*REMUNIT + 'px';

                }

                setBodyFontSize();

            }

        }(window,document)