document.addEventListener("DOMContentLoaded", function () { const target = document.querySelector(".sec_vis_filt"); const button = document.querySelector(".btn_flt_filtro"); if (!target || !button) return; const observer = new IntersectionObserver( (entries) => { entries.forEach((entry) => { if (!entry.isIntersecting) { // salió del viewport button.classList.add("active"); } else { // volvió a entrar button.classList.remove("active"); } }); }, { threshold: 0 } ); observer.observe(target); });