1var siteHeader = document.getElementById('siteHeader'),
2    siteNav = document.getElementById('siteNav');
3
4    window.onscroll = function() {
5        if ( siteNav.offsetTop < document.documentElement.scrollTop + 26 || siteNav.offsetTop < document.body.scrollTop + 26) {
6            siteHeader.setAttribute("class","sticky");
7        }
8        else {
9            siteHeader.setAttribute("class","");
10        }
11    }
12

1nav {
2	position:sticky;
3	top:0;
4}
5
6/*Top can be replaced with bottom, left, or right 
7	depending on what you want :) */