$(function(){
    $("html").css("font-size", $(window).width() >= 750 ? 100 : $(window).width() / 750 * 100 + "px");
    $(window).resize(function () {
        $("html").css("font-size", $(window).width() >= 750 ? 100 : $(window).width() / 750 * 100 + "px");
    });
});