(function(){
    ‘use strict‘;
    
    setRemUnit();
    window.addEventListener(‘resize‘,setRemUnit);
    function setRemUnit(){
        var docEl = document.documentElement;
        var ratio = 18.75;
        var viewWidth = docEl.getBoundingClientRect().width || window.innerWidth;
        docEl.style.fontSize = viewWidth / ratio + ‘px‘;
    }
})();