05Staggered items

<main class="stage">
  <nav class="menu is-demo">
    <button class="menu__trigger" type="button" aria-expanded="false">Settings</button>
    <ul class="menu__panel">
      <li><a href="#">General</a></li>
      <li><a href="#">Security</a></li>
      <li><a href="#">Notifications</a></li>
      <li><a href="#">Billing</a></li>
    </ul>
  </nav>
</main>

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

$duration: $dur-quick;                             // 항목 하나가 나타나는 시간
$easing: $ease-out;                                // 시작 빠르고 끝은 부드럽게
$stagger: 20ms;                                    // 항목 사이 시차

$color: $subject-blue-deep;                        // 트리거 버튼 색 (크림 글자가 얹히므로 진한 파랑)

@include stage($stage-ink);

.menu {
  position: relative;
  align-self: flex-start;                            // 패널이 4개 항목만큼 길어 트리거를 무대 중앙에 두면 아래로 넘친다 — 위로 붙여 여유를 둔다 (실측 320px 재검증 2026-09-10)
  font-weight: 500;
  font-size: clamp(13px, 3.6vw, 16px);
  line-height: 1.4;
  font-family: inherit;

  &__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;
  }

  &__panel {
    position: absolute;
    top: calc(100% + 8px);
    left: 0;
    width: max-content;
    max-width: min(160px, 78vw);
    margin: 0;
    padding: 6px;
    list-style: none;
    background: $subject-cream;
    border-radius: $r-card;
    box-shadow: $shadow-raised;
    visibility: hidden;
  }
  &.is-open &__panel,
  &.is-demo &__panel { visibility: visible; }

  &__panel li a {
    display: block;
    padding: 6px 12px;                                 // 320px 재검증: align-self:flex-start 로도 4항목분 높이가 8px 모자랐다 — 항목당 4px(2px×2) 씩 줄여 20px 확보 (실측 2026-09-10)
    border-radius: $r-control - 4px;
    color: $stage-ink;
    text-decoration: none;
  }
  &__panel li a:hover { background: rgba($stage-ink, .06); }

  // 항목마다 20ms 씩 늦게 등장 — transform · opacity 만 움직인다
  &__panel li { opacity: 0; transform: translateY(-6px); }
  &.is-open &__panel li { opacity: 1; transform: none; transition: opacity $duration $easing, transform $duration $easing; }
  &.is-demo &__panel li { animation: item-loop $dur-loop $easing infinite; }

  @for $i from 1 through 4 {
    &.is-open &__panel li:nth-child(#{$i}) { transition-delay: ($i - 1) * $stagger; }
    &.is-demo &__panel li:nth-child(#{$i}) { animation-delay: ($i - 1) * $stagger; }
  }
}

@keyframes item-loop {
  0%, 30%   { opacity: 0; transform: translateY(-6px); }
  40%, 78%  { opacity: 1; transform: none; }
  88%, 100% { opacity: 0; transform: translateY(-6px); }
}

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

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.menu {
  position: relative;
  align-self: flex-start;
  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 {
  position: absolute;
  top: calc(100% + 8px);
  left: 0;
  width: max-content;
  max-width: min(160px, 78vw);
  margin: 0;
  padding: 6px;
  list-style: none;
  background: #fff7e6;
  border-radius: 16px;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  visibility: hidden;
}
.menu.is-open .menu__panel, .menu.is-demo .menu__panel {
  visibility: visible;
}
.menu__panel li a {
  display: block;
  padding: 6px 12px;
  border-radius: 8px;
  color: #17141a;
  text-decoration: none;
}
.menu__panel li a:hover {
  background: rgba(23, 20, 26, 0.06);
}
.menu__panel li {
  opacity: 0;
  transform: translateY(-6px);
}
.menu.is-open .menu__panel li {
  opacity: 1;
  transform: none;
  transition: opacity 220ms ease-out, transform 220ms ease-out;
}
.menu.is-demo .menu__panel li {
  animation: item-loop 2s ease-out infinite;
}
.menu.is-open .menu__panel li:nth-child(1) {
  transition-delay: 0ms;
}
.menu.is-demo .menu__panel li:nth-child(1) {
  animation-delay: 0ms;
}
.menu.is-open .menu__panel li:nth-child(2) {
  transition-delay: 20ms;
}
.menu.is-demo .menu__panel li:nth-child(2) {
  animation-delay: 20ms;
}
.menu.is-open .menu__panel li:nth-child(3) {
  transition-delay: 40ms;
}
.menu.is-demo .menu__panel li:nth-child(3) {
  animation-delay: 40ms;
}
.menu.is-open .menu__panel li:nth-child(4) {
  transition-delay: 60ms;
}
.menu.is-demo .menu__panel li:nth-child(4) {
  animation-delay: 60ms;
}

@keyframes item-loop {
  0%, 30% {
    opacity: 0;
    transform: translateY(-6px);
  }
  40%, 78% {
    opacity: 1;
    transform: none;
  }
  88%, 100% {
    opacity: 0;
    transform: translateY(-6px);
  }
}
@media (prefers-reduced-motion: reduce) {
  .menu__panel li {
    transition: none !important;
  }
  .menu.is-demo .menu__panel li {
    animation: none;
    opacity: 0;
    transform: none;
  }
  .menu.is-demo .menu__panel {
    visibility: hidden;
  }
}

// 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 "./StaggerItemsDropdown.module.scss";

export type StaggerItemsDropdownProps = {
  triggerLabel: string;
  items: string[];
  /** 항목 하나가 나타나는 시간 (기본 220ms) */
  duration?: number;
  easing?: string;
  /** 항목 사이 시차 ms (기본 20ms) */
  stagger?: number;
  color?: string;
};

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

export default function StaggerItemsDropdown({
  triggerLabel,
  items,
  duration = 220,
  easing = "ease-out",
  stagger = 20,
  color = "#0a4fe8",
}: StaggerItemsDropdownProps) {
  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} ${styles.panelOpen}` : styles.panel}>
        {items.map((label, i) => (
          <li key={label} style={{ transitionDelay: open ? `${i * stagger}ms` : "0ms" }}>
            <a href="#">{label}</a>
          </li>
        ))}
      </ul>
    </nav>
  );
}