const detailsElements = document.getElementsByTagName("details");
const dropdown = Array.from(detailsElements);

const save = () => {
	dropdown.forEach((details, i) => {
		localStorage.setItem(`details${i}`, details.hasAttribute("open"));
	});
};

dropdown.forEach((details, i) => {
	const isOpen = JSON.parse(localStorage.getItem(`details${i}`)) || false;
	details.toggleAttribute("open", isOpen);
	details.addEventListener("toggle", save);
});