document.addEventListener('DOMContentLoaded', () => {
  const els = document.querySelectorAll('.reveal');
  const io = new IntersectionObserver((entries)=>{
    entries.forEach(entry=>{
      if(entry.isIntersecting){
        entry.target.classList.add('visible');
        io.unobserve(entry.target);
      }
    });
  }, {threshold:0.12});
  els.forEach(el=>io.observe(el));
});