document.addEventListener('DOMContentLoaded', function() {
  window.addEventListener('scroll', myFunctionForSticky);
  // Get the navbar
  var navbar = document.getElementById("masthead");
  var sticky = navbar.offsetTop+100;

  // Add the sticky class to the navbar when you reach its scroll position. 
  // Remove "sticky" when you leave the scroll position
  function myFunctionForSticky() {
    if (window.pageYOffset >= sticky) {
      navbar.classList.add("sticky");
    } else {
      navbar.classList.remove("sticky");
    }
  }
});