GitHub Header Toggler

toggle-header.js

// Original:
(function(doc, className) {
  var header = doc.querySelector('[role=banner]'),
    button = doc.createElement('button'),
    classList = header.classList,
    light = className + 'light',
    dark = className + 'dark',
    isLight
  button.className = 'btn'
  button.style = 'position:sticky;bottom:1em;left:1em'
  button.innerHTML = 'Toggle Header'
  button.onclick = function() {
    isLight = classList.contains(light)
    classList.remove(isLight ? light : dark)
    classList.add(isLight ? dark : light)
  };
  header.parentNode.appendChild(button)
})(document, 'header-')


// Min:
!function(e,t){var n,o=e.querySelector("[role=banner]"),a=e.createElement("button"),r=o.classList,c=t+"light",i=t+"dark";a.className="btn",a.style="position:sticky;bottom:1em;left:1em",a.innerHTML="Toggle Header",a.onclick=function(){n=r.contains(c),r.remove(n?c:i),r.add(n?i:c)},o.parentNode.appendChild(a)}(document,"header-");