賢威のサイドバーのカテゴリー表示をアコーディオンにする方法

.cat-item .children {
max-height: 0;
overflow: hidden;
transition: max-height 0.8s ease;
}

.cat-item.nyactive > .children {
display: block;
}

.cat-item > a {
cursor: pointer;
}

<script>
document.addEventListener('DOMContentLoaded', function () {
const parentItems = document.querySelectorAll('.cat-item');
parentItems.forEach(function (item) {
const childList = item.querySelector('.children');
const link = item.querySelector('a');

if (childList && link) {
// 初期状態
childList.style.maxHeight = '0px';

// クリック（スマホ・PC共通）
link.addEventListener('click', function (e) {
e.preventDefault();
const isOpen = item.classList.contains('nyactive');

// 他を閉じる
document.querySelectorAll('.cat-item.nyactive').forEach(function (activeItem) {
const activeChild = activeItem.querySelector('.children');
activeChild.style.maxHeight = '0px';
activeItem.classList.remove('nyactive');
});

if (!isOpen) {
item.classList.add('nyactive');
childList.style.maxHeight = childList.scrollHeight + 'px';
}
});

// PC限定：マウスオーバーで開く
item.addEventListener('mouseenter', function () {
if (window.innerWidth >= 768) {
item.classList.add('nyactive');
childList.style.maxHeight = childList.scrollHeight + 'px';
}
});

item.addEventListener('mouseleave', function () {
if (window.innerWidth >= 768) {
item.classList.remove('nyactive');
childList.style.maxHeight = '0px';
}
});
}
});
});
</script>