08Dùng thuộc tính popover gốc

<main class="stage">
  <div class="menu">
    <button class="menu__trigger" type="button" popovertarget="menu-panel">Tùy chọn</button>
    <ul class="menu__panel" id="menu-panel" popover>
      <li><a href="#">Chia sẻ</a></li>
      <li><a href="#">Đánh dấu</a></li>
      <li><a href="#">Báo cáo</a></li>
    </ul>
  </div>
</main>

@use "../../../../site/static/demo-tokens" as *;

$duration: $dur-base;                              // 내용이 접혔다 펴지는 시간
$easing: $ease-pop;                                // 살짝 튀는 이징
$color: $subject-blue-deep;                        // 트리거 버튼 색 (크림 글자가 얹히므로 진한 파랑)

@include stage($stage-paper);

.menu {
  position: relative;
  font-weight: 500;
  font-size: clamp(13px, 3.6vw, 16px);
  line-height: 1.4;
  font-family: inherit;
}

.menu__trigger {
  border: 0;
  border-radius: $r-control;
  padding: clamp(9px, 3vw, 13px) clamp(16px, 4vw, 22px);
  font-weight: 700;
  font-family: inherit;
  color: $subject-cream;
  background: $color;
  cursor: pointer;
}

.menu__panel {
  width: max-content;
  max-width: min(150px, 70vw);
  margin: 0;
  padding: 6px;
  list-style: none;
  border: 0;
  border-radius: $r-card;
  background: $subject-cream;
  box-shadow: $shadow-raised;
  transform: scale(.9);
  opacity: 0;
}

.menu__panel li a {
  display: block;
  padding: 8px 12px;
  border-radius: $r-control - 4px;
  color: $stage-ink;
  text-decoration: none;
}
.menu__panel li a:hover { background: rgba($stage-ink, .06); }

.menu__panel::backdrop {
  background: rgba($stage-ink, .18);
}

// popover 는 열어 둔 채, 안쪽 내용만 2초 주기로 접었다 편다 (transform · opacity 만 움직인다)
.menu__panel:popover-open { animation: pop-loop $dur-loop $easing infinite; }

@keyframes pop-loop {
  0%, 30%   { transform: scale(.9); opacity: 0; }
  45%, 80%  { transform: scale(1); opacity: 1; }
  95%, 100% { transform: scale(.9); opacity: 0; }
}

@media (prefers-reduced-motion: reduce) {
  .menu__panel { transition: none !important; }
  .menu__panel:popover-open { animation: none; transform: scale(1); opacity: 1; }
}

html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffffff;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.menu {
  position: relative;
  font-weight: 500;
  font-size: clamp(13px, 3.6vw, 16px);
  line-height: 1.4;
  font-family: inherit;
}

.menu__trigger {
  border: 0;
  border-radius: 12px;
  padding: clamp(9px, 3vw, 13px) clamp(16px, 4vw, 22px);
  font-weight: 700;
  font-family: inherit;
  color: #fff7e6;
  background: #0a4fe8;
  cursor: pointer;
}

.menu__panel {
  width: max-content;
  max-width: min(150px, 70vw);
  margin: 0;
  padding: 6px;
  list-style: none;
  border: 0;
  border-radius: 16px;
  background: #fff7e6;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  transform: scale(0.9);
  opacity: 0;
}

.menu__panel li a {
  display: block;
  padding: 8px 12px;
  border-radius: 8px;
  color: #17141a;
  text-decoration: none;
}

.menu__panel li a:hover {
  background: rgba(23, 20, 26, 0.06);
}

.menu__panel::backdrop {
  background: rgba(23, 20, 26, 0.18);
}

.menu__panel:popover-open {
  animation: pop-loop 2s cubic-bezier(0.2, 1.4, 0.4, 1) infinite;
}

@keyframes pop-loop {
  0%, 30% {
    transform: scale(0.9);
    opacity: 0;
  }
  45%, 80% {
    transform: scale(1);
    opacity: 1;
  }
  95%, 100% {
    transform: scale(0.9);
    opacity: 0;
  }
}
@media (prefers-reduced-motion: reduce) {
  .menu__panel {
    transition: none !important;
  }
  .menu__panel:popover-open {
    animation: none;
    transform: scale(1);
    opacity: 1;
  }
}

// popover 는 열려야 화면에 그려진다. 열어 둔 채 안쪽 내용만 2초 주기로 접었다 편다.
// 트리거는 popovertarget 하나로 실제 열고 닫기·바깥 클릭·Esc 를 브라우저가 대신 처리한다.
document.getElementById('menu-panel').showPopover();

import { useState } from "react";
import type { CSSProperties } from "react";
import styles from "./PopoverNativeDropdown.module.scss";

export type PopoverNativeDropdownProps = {
  triggerLabel: string;
  items: string[];
  /** 내용이 접혔다 펴지는 시간 (기본 300ms) */
  duration?: number;
  easing?: string;
  color?: string;
};

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };

export default function PopoverNativeDropdown({
  triggerLabel,
  items,
  duration = 300,
  easing = "cubic-bezier(.2,1.4,.4,1)",
  color = "#2f6df6",
}: PopoverNativeDropdownProps) {
  const [open, setOpen] = useState(false);
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };

  return (
    <div className={styles.menu} style={vars}>
      <button type="button" className={styles.trigger} aria-expanded={open} onClick={() => setOpen((v) => !v)}>
        {triggerLabel}
      </button>
      {/* React 는 showPopover() 를 ref 로 직접 불러야 해서 상태로 대신한다. 실제 zip 의 vanilla 판은 popover 속성 + popovertarget 을 그대로 쓴다 */}
      <ul className={open ? `${styles.panel} ${styles.panelOpen}` : styles.panel}>
        {items.map((label) => (
          <li key={label}><a href="#">{label}</a></li>
        ))}
      </ul>
    </div>
  );
}