HTMLのPopover APIでメニューを作る方法【popovertarget・開閉制御】

<main class="demo-card">
  <img class="nines-logo" src="https://kjnine.com/wp-content/themes/kjnines_theme/images/svg2/nines_logo.svg" alt="NINES">
  <p class="eyebrow">NATIVE POPOVER</p>
  <h1>プロフィールメニュー</h1>

  <button class="menu-button" type="button" popovertarget="profileMenu">
    メニューを開く
  </button>

  <nav id="profileMenu" class="profile-menu" popover aria-label="プロフィールメニュー">
    <a href="#profile">プロフィール</a>
    <a href="#settings">設定</a>
    <button type="button" data-logout>ログアウト</button>
  </nav>
</main>

* {
  box-sizing: border-box;
}

body {
  min-height: 100vh;
  margin: 0;
  display: grid;
  place-items: center;
  padding: 24px;
  background: #eef2f7;
  color: #111;
  font-family: system-ui, sans-serif;
}

.demo-card {
  position: relative;
  width: min(100%, 520px);
  padding: 40px;
  border: 1px solid #dce2ec;
  background: #fff;
}

.nines-logo {
  position: absolute;
  top: 18px;
  right: 18px;
  width: 58px;
  opacity: 0.16;
}

.eyebrow {
  color: #0057ff;
  font-size: 0.78rem;
  font-weight: 800;
  letter-spacing: 0.14em;
}

.menu-button {
  min-height: 44px;
  padding: 10px 16px;
  border: 0;
  background: #0057ff;
  color: #fff;
  cursor: pointer;
  font: inherit;
  font-weight: 800;
}

.profile-menu {
  width: min(260px, calc(100vw - 32px));
  margin: auto;
  padding: 8px;
  border: 1px solid #cfd6e3;
  background: #fff;
  box-shadow: 0 18px 50px rgb(15 30 60 / 22%);
}

.profile-menu a,
.profile-menu button {
  display: block;
  width: 100%;
  padding: 12px;
  border: 0;
  background: transparent;
  color: #111;
  text-align: left;
  text-decoration: none;
  cursor: pointer;
  font: inherit;
}

.profile-menu a:hover,
.profile-menu button:hover,
.profile-menu a:focus-visible,
.profile-menu button:focus-visible {
  background: #edf3ff;
  outline: 2px solid #0057ff;
  outline-offset: -2px;
}

@media (prefers-reduced-motion: no-preference) {
  .profile-menu:popover-open {
    animation: popover-in 160ms ease-out;
  }

  @keyframes popover-in {
    from {
      opacity: 0;
      transform: translateY(-8px) scale(0.98);
    }
  }
}

const menu = document.querySelector('#profileMenu');
const logoutButton = document.querySelector('[data-logout]');

menu.addEventListener('toggle', (event) => {
  console.log(`Popover is now ${event.newState}`);
});

logoutButton.addEventListener('click', () => {
  menu.hidePopover();
  alert('ログアウト処理へ進みます。');
});