_auto_hide_reveal_header.md

Header will need to be set to sticky and overlay by default.

Simply add this script to your global JS or enque as a seperate script file.

auto_hide_reveal_header.js

window.onscroll = function(e) { 
    var scrollY = window.pageYOffset || document.documentElement.scrollTop;
    var header = document.querySelector('header');
    var height = -header.clientHeight;
    header.style.transition = 'transform 0.5s';

    (scrollY <= Math.max(this.lastScroll, 300) || window.innerWidth <= 200 || this.loaded === undefined)
      ? header.style.transform = 'translateY(0px)'
      : header.style.transform = 'translateY(' + height + 'px)';

    this.lastScroll = scrollY;
    this.loaded = true;
};

Thanks Abby, Small world. Check out some of Zach's gists, he has a great assortment of BB snippets. https://gist.github.com/zackpyle and he created this nice plugin for class management https://github.com/zackpyle/BBClassDropdown