03Phóng to từ góc (transform-origin)

<main class="stage">
  <div class="toolbar">
    <nav class="menu is-demo">
      <button class="menu__trigger" type="button" aria-expanded="false">Hồ sơ</button>
      <ul class="menu__panel">
        <li><a href="#">Cài đặt tài khoản</a></li>
        <li><a href="#">Thông báo</a></li>
        <li><a href="#">Đăng xuất</a></li>
      </ul>
    </nav>
  </div>
</main>

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

$duration: $dur-quick;                             // 확대되는 시간
$easing: $ease-pop;                                // 살짝 튀는 이징
$color: $subject-cream;                            // 트리거 버튼 색 (주황 무대와 대비)

@include stage($stage-orange);

.toolbar {
  width: min(280px, 92vw);
  display: flex;
  justify-content: flex-end;
  align-self: flex-start;                            // 패널이 트리거 아래로 열려 무대 중앙에 두면 320px 에서 아래로 넘친다 — 위로 붙여 여유를 둔다 (실측 320px 재검증 2026-09-10)
}

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

  &__trigger {
    border: 0;
    border-radius: $r-pill;
    padding: clamp(9px, 3vw, 12px) clamp(16px, 4vw, 20px);
    font-weight: 700;
    font-family: inherit;
    color: $stage-ink;
    background: $color;
    cursor: pointer;
  }

  &__panel {
    position: absolute;
    top: calc(100% + 8px);
    right: 0;                                        // 트리거가 붙은 모서리
    width: max-content;
    max-width: min(170px, 76vw);
    margin: 0;
    padding: 6px;
    list-style: none;
    background: $subject-cream;
    border-radius: $r-card;
    box-shadow: $shadow-raised;
    transform-origin: top right;                      // 트리거 모서리를 기준으로 확대
    transform: scale(.9);
    opacity: 0;
    pointer-events: none;
  }

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

  &.is-open &__panel { opacity: 1; transform: scale(1); pointer-events: auto; transition: opacity $duration $easing, transform $duration $easing; }
  &.is-demo &__panel { animation: reveal-loop $dur-loop $easing infinite; }
}

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

@media (prefers-reduced-motion: reduce) {
  .menu__panel { transition: none !important; }
  .menu.is-demo .menu__panel { animation: none; opacity: 0; transform: scale(.9); }
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ff4d1f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.toolbar {
  width: min(280px, 92vw);
  display: flex;
  justify-content: flex-end;
  align-self: flex-start;
}

.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: 999px;
  padding: clamp(9px, 3vw, 12px) clamp(16px, 4vw, 20px);
  font-weight: 700;
  font-family: inherit;
  color: #17141a;
  background: #fff7e6;
  cursor: pointer;
}
.menu__panel {
  position: absolute;
  top: calc(100% + 8px);
  right: 0;
  width: max-content;
  max-width: min(170px, 76vw);
  margin: 0;
  padding: 6px;
  list-style: none;
  background: #fff7e6;
  border-radius: 16px;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  transform-origin: top right;
  transform: scale(0.9);
  opacity: 0;
  pointer-events: none;
}
.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.is-open .menu__panel {
  opacity: 1;
  transform: scale(1);
  pointer-events: auto;
  transition: opacity 220ms cubic-bezier(0.2, 1.4, 0.4, 1), transform 220ms cubic-bezier(0.2, 1.4, 0.4, 1);
}
.menu.is-demo .menu__panel {
  animation: reveal-loop 2s cubic-bezier(0.2, 1.4, 0.4, 1) infinite;
}

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

// 트리거를 클릭하면 열리고 닫힌다. 데모(.is-demo)는 스스로 반복한다.
var m = document.querySelector('.menu'), t = m.querySelector('.menu__trigger');
t.addEventListener('click', function () {
  m.classList.remove('is-demo');
  t.setAttribute('aria-expanded', m.classList.toggle('is-open'));
});

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

export type ScaleOriginDropdownProps = {
  triggerLabel: string;
  items: string[];
  /** 확대되는 시간 (기본 220ms) */
  duration?: number;
  easing?: string;
  color?: string;
};

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

export default function ScaleOriginDropdown({
  triggerLabel,
  items,
  duration = 220,
  easing = "cubic-bezier(.2,1.4,.4,1)",
  color = "#fff7e6",
}: ScaleOriginDropdownProps) {
  const [open, setOpen] = useState(false);
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };

  return (
    <nav className={styles.menu} style={vars}>
      <button type="button" className={styles.trigger} aria-expanded={open} onClick={() => setOpen((v) => !v)}>
        {triggerLabel}
      </button>
      <ul className={open ? `${styles.panel} ${styles.panelOpen}` : styles.panel}>
        {items.map((label) => (
          <li key={label}><a href="#">{label}</a></li>
        ))}
      </ul>
    </nav>
  );
}