let observer = new IntersectionObserver((entries, observer) => {
    entries.forEach(entry => {
        if(entry.isIntersecting){
            entry.target.classList.add('element-show');
            observer.unobserve(entry.target);
        }
    });
}, {rootMargin: "3% 0px"});

document.querySelectorAll('section .block__img').forEach((el) => {observer.observe(el)});