document.querySelectorAll('.animatein :is(h1, h2, h3, p, img, .wp-block-buttons').forEach(function (el) {

    const threshold = 0.5;
    el.style.opacity = 0;
    const once = 1;
	
    const observer = new IntersectionObserver(function (entries) {
        if (entries[0].intersectionRatio === 0) {
            el.classList.remove(el.getAttribute('animatein'));
            return;
        }
        if (entries[0].intersectionRatio < Number(threshold)) {
            return;
        }
        el.classList.add('animate-in-view');
        Number(once) && observer.unobserve(el);
    }, { threshold: [Number(threshold), 0] });
    observer.observe(el);
});