text: import jump from 'jump.js';
  import { select, scrollY, easeOutQuint } from '../deps/utils';
  
  const backToTopButton = select('.back-to-top-button');
  
  window.addEventListener('scroll', () => {
    backToTopButton.classList[scrollY() > 500 ? 'add' : 'remove']('is-visible');
  });
  
  backToTopButton.onclick = () => {
    jump('.header', {
      duration: 750,
      easing: easeOutQuint
    });
  };
  