adds class 'stuck' to elements that are stuck. Uses Bootstraps' `position-sticky` class as a selector.

hnl.stickyStuck

const stickes = document.body.querySelectorAll('.position-sticky');

window.addEventListener('scroll', function(){
  stickes.forEach(function(el){
    el.classList.toggle('stuck', el.getBoundingClientRect().top === parseInt(window.getComputedStyle(el).top, 10));
  });
});