h5 rem

<script>
    (function(){
    setRem();
    window.addEventListener('orientation' in window?"deviceorientation":"resize",setRem);
    function setRem(){
        var html = document.getElementsByTagName('html')[];
        var pageWidth = html.getBoundingClientRect().width;
        html.style.fontSize = pageWidth /+ 'px';
    }
})();

</script>